UNIVERSITY  OF  CALIFORNIA 
AT  LOS  ANGELES 


THE 
ABSORPTION  SPECTRA  OF  SOLUTIONS 

OF  COMPARATIVELY  RARE  SALTS 

INCLUDING  THOSE  OF  GADOLINIUM,  DYSPROSIUM,  AND  SAMARIUM 
THE  SPECTROPHOTOGRAPHY  OF  CERTAIN  CHEMICAL  REACTIONS 

AND  THE  EFFECT  OF  HIGH  TEMPERATURE  ON  THE  ABSORPTION  SPECTRA 
OF  NON-AQUEOUS  SOLUTIONS 


BY 
HAEEY  C.  JONES  AND  W.  W.  STKONG 


WASHINGTON,  D.  C. 

PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OP  WASHINGTON 
1911 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
PUBLICATION  No.  160 


PRESS  OF  J.  B.  LIPPINCOTT  COMPANY 
PHILADELPHIA 


J  7  / 


THE  ABSORPTION  SPECTRA  OF  SOLUTIONS 

OF  COMPAEATIVELY  EAEE  SALTS 

INCLUDING  THOSE   OF  GADOLINIUM,  DYSPROSIUM,  AND  SAMARIUM 
THE  SPECTROPHOTOGRAPHY  OF  CERTAIN  CHEMICAL  REACTIONS 

AND  THE  EFFECT  OF  HIGH  TEMPERATURE  ON  THE  ABSORPTION  SPECTRA 
OF  NON-AQUEOUS  SOLUTIONS 


BY 

HAREY  C.  JONES  AND  W.  W.  STEONG 


209174 


PREFACE. 

The  work  recorded  in  this  monograph  on  the  absorption  spectra  of  solu- 
tions is  a  continuation  of  that  already  published  by  Jones  and  Uhler  (Publi- 
cation No.  60,  Carnegie  Institution  of  Washington),  Jones  and  Anderson 
(Publication  No.  110,  Carnegie  Institution  of  Washington),  and  Jones  and 
Strong  (Publication  No.  130,  Carnegie  Institution  of  Washington).  This 
work,  like  that  recorded  in  the  preceding  publications,  has  been  made  possible 
by  grants  awarded  by  the  Carnegie  Institution  of  Washington. 

The  attempt  has  been  made  in  this  work  to  solve  three  problems: 

First,  to  map  out  the  absorption  spectra  of  certain  comparatively  rare 
substances.  Urbain  has  generously  forwarded  Dr.  Strong  ample  quantities  of 
the  oxides  of  gadolinium,  dysprosium,  and  samarium  with  which  to  prepare 
their  salts  and  study  their  spectra.  We  find  that  the  salts  of  dysprosium  and 
samarium  have  spectra  that  are  almost  as  interesting  as  those  of  neodymium, 
with  very  sharp,  characteristic  bands. 

Second.  Under  the  spectrophotography  of  chemical  reactions  we  have 
studied  especially  the  effect  of  oxidizing  agents  on  uranous  salts.  We  have 
used  milder  oxidizing  agents  and  stronger  oxidizing  agents,  and  have  dissolved 
the  uranous  salt  in  single  solvents  and  in  mixed  solvents.  When  uranous 
chloride  is  dissolved  in  a  mixture  of  alcohol  and  water,  both  the  "alcohol"  and 
the  "water"  bands  come  out  simultaneously  on  the  plate.  A  mild  oxidizing 
agent  was  found  to  oxidize  the  "hydrated"  salts  and  to  leave  unaffected 
the  "  alcoholated "  salts.  A  strong  oxidizing  agent,  on  the  other  hand,  oxi- 
dized both  the  "hydrated"  and  the  "alcoholated"  uranous  salt  to  the  uranyl 
condition.  This  is,  therefore,  an  example  of  "selective  oxidation." 

Third.  By  means  of  the  closed  cell  we  have  been  able  to  study  the  absorp- 
tion spectra  of  solutions  in  methyl  and  ethyl  alcohols  up  to  temperatures  as 
high  as  195°.  The  absorption  bands  widen  with  rise  in  temperature  up  to  the 
highest  temperatures  employed.  Colored  solutions,  therefore,  become  more 
and  more  nearly  opaque  as  the  temperature  to  which  the  solutions  are  sub- 
jected is  raised. 

The  effect  of  rise  in  temperature  on  the  absorption  spectra  of  neodym- 
ium salts  in  mixtures  of  alcohol  and  water,  where  both  the  "alcohol"  and 
the  "water"  bands  appear  simultaneously,  has  been  studied.  The  "water" 
bands  are  more  affected  by  rise  in  temperature  than  the  "alcohol"  bands, 
showing  that  the  "hydrates"  are  less  stable  with  rise  in  temperature  than  the 
"alcoholates." 

The  problems  now  under  investigation  include  the  effect  of  ions  as  com- 
pared with  molecules  on  the  absorption  spectra  of  solutions,  the  effect  of 
high  temperature  on  the  absorption  spectra  of  aqueous  solutions,  and  the 
measurement  of  the  intensity  of  the  various  absorption  bands  by  means  of 
the  radiomicrometer  and  thermoelectric  junctions. 

It  gives  me  special  pleasure  to  express  my  indebtedness  and  thanks  to 
the  Carnegie  Institution  of  Washington  for  the  generous  support  which  they 


VI  PREFACE. 

have  given  this  work  in  the  past  and  for  the  aid  which  they  have  tendered  for 
the  future. 

I  wish  to  express  my  thanks  to  Professor  J.  S.  Ames  for  ample  space  in 
the  Physical  Laboratory  for  carrying  out  the  physical  part  of  this  work;  to 
Professor  J.  A.  Anderson  for  a  large  number  of  valuable  suggestions  in  con- 
nection with  the  work;  to  Professor  A.  H.  Pfund  for  advice  in  connection  with 
the  construction  of  the  radiomicrometer;  and  to  Dr.  J.  Sam  Guy,  who  will 
continue  this  work,  for  aid  especially  in  preparing  the  various  salts  and  solu- 
tions of  the  salts  of  dysprosium  and  samarium. 

HARRY  C.  JONES. 
JONE  1911. 


CONTENTS. 


PAGE. 

CHAPTER  I.    THE  ABSORPTION  AND  EMISSION  CENTERS  OF  LIGHT  AND  HEAT: 

Atomic  Structure  and  Spectra 1 

The  lonization  Theory  and  Absorption  and  Emission  Centers 2 

Sulphur  Bands 3 

The  Carriers  of  Canal-Ray  Spectra 4 

The  Carriers  of  Spark  Spectra 5 

The  Emission  Centers  of  Flames  and  Arcs 6 

Schumann  Waves 6 

The  Possible  Catalytic  Action  of  Light 6 

Emission  Spectra  of  Organic  Compounds 7 

The  Absorption  Spectra  of  Organic  Compounds 8 

The  Unit  of  this  Absorption 8 

The  Theory  of  Chromophores 10 

Influence  of  the  Solvent 15 

The  Absorption  Spectra  of  Benzene  and  Its  Derivatives 16 

Theory  of  Dynamic  Isomerism 18 

Theory  of  Stark 23 

Other  Benzene  Theories 24 

CHAPTER  II.    EXPERIMENTAL  METHODS  AND  APPARATUS: 

CHAPTER  III.     MAPPING  THE  ABSORPTION  SPECTRA  OF  VARIOUS  SALTS  IN  SOLUTION: 

The  Absorption  of  Certain  Cyanides  and  Chromates 31 

Calcium  Ferrocyanide  and  Calcium  Ferricyanide 32 

The  Chromate  and  Bichromate  of  Lithium 33 

Aluminium  and  Calcium  Chromates 33 

Potassium  Nickel  Chromate  and  Copper  Bichromate 33 

The  Absorption  of  Solutions  of  Certain  Erbium  Salts 33 

The  Absorption  of  Solutions  of  Certain  Neodymium  Salts 34 

Neodymium  Chloride  in  Water 35 

Neodymium  Chloride  as  a  Methyl  Alcoholate 35 

Neodymium  Chloride  in  Propyl  Alcohol 36 

Neodymium  Chloride  in  Isopropyl  Alcohol 36 

Neodymium  Chloride  in  Butyl  Alcohol 36 

Neodymium  Chloride  in  Isobutyl  Alcohol 37 

Neodymium  Chloride  in  Ether 37 

Neodymium  Nitrate  in  Propyl  Alcohol 38 

Neodymium  Nitrate  in  Isopropyl  Alcohol 38 

Neodymium  Nitrate  in  Butyl  Alcohol 38 

Neodymium  Nitrate  in  Isobutyl  Alcohol 39 

Neodymium  Nitrate  in  Acetone 39 

Neodymium  Nitrate  in  Ethyl  Ester 39 

Neodymium  Acetate  in  Acetone 40 

Neodymium  Acetate  in  Formamide 40 

Summary  of  Neodymium  Spectra 40 

The  Absorption  Spectrum  of  Solutions  of  Certain  Salts  of  Uranium 43 

Uranyl  Chloride  in  Propyl  Alcohol 43 

Uranyl  Chloride  in  Isopropyl  Alcohol 43 

Uranyl  Chloride  in  Butyl  Alcohol 43 

Uranyl  Chloride  in  Isobutyl  Alcohol 43 

Uranyl  Chloride  in  Ether 43 

Uranyl  Chloride  in  Methyl  Ester 44 

Uranyl  Chloride  in  Ethyl  Ester 44 

Uranyl  Chloride  in  Formamide 44 

Uranyl  Nitrate  in  Propyl  Alcohol 44^ 

Uranyl  Nitrate  in  Acetone 44' 

Uranyl  Nitrate  in  Methyl  Ester 44 

Uranous  Chloride  in  Propyl  Alcohol 

Uranous  Chloride  in  Isobutyl  Alcohol 45 

Uranous  Chloride  hi  Methyl  Ester 45 

The  Absorption  Centers  of  Uranium  Spectra ' 

The  Absorption  Spectrum  of  Gadolinium 46 

Gadolinium  Chloride  in  Water 46 

Gadolinium  Chloride  in  Ethyl  Alcohol 46 

vii 


Vlll  CONTENTS. 

CHAPTER  III — continued.  PAGE. 

The  Absorption  Spectrum  of  Dysprosium 46 

Dysprosium  Chloride  in  Water 47 

Dysprosium  Chloride  in  Methyl  Alcohol 47 

Dysprosium  Chloride  in  Ethyl  Alcohol 47 

Dysprosium  Acetate  in  Water 48 

The  Absorption  Spectrum  of  Samarium 48 

Samarium  Chloride  in  Water 48 

Samarium  Nitrate  in  Water 49 

Samarium  Chloride  in  Methyl  and  Ethyl  Alcohols 49 

Samarium  Chloride  in  Water  and  Ethyl  Alcohol 50 

CHAPTER  IV.     THE  SPECTROPHOTOGRAPHY  OF  CHEMICAL  REACTIONS: 

Introduction 51 

Phosphorescence  of  Praseodymium  in  Calcium  Oxide 54 

Phosphorescence  of  Neodymium  in  Calcium  Oxide 54 

Phosphorescence  of  Erbium  in  Calcium  Oxide 54 

Phosphorescence  of  Praseodymium  in  Calcium  Sulphate 54 

Phosphorescence  of  Erbium  in  Calcium  Sulphate 54 

Phosphorescence  of  Erbium  in  Calcium  Fluoride 54 

Neodymium  Chloride  in  Ethyl  Acetate  and  Anthracene 56 

The  Uranyl  and  Uranous  Bands .' 57 

The  Oxidization  of  Uranous  to  Uranyl  Salts  in  Solution 58 

The  Oxidization  of  Uranous  Chloride  by  Hydrogen  Peroxide 58 

Oxidization  of  Uranous  Chloride  in  Hydrochloric  Acid  by  Hydrogen  Peroxide ....  60 

The  Oxidization  of  Uranous  Sulphate 61 

The  Oxidization  of  Uranous  Bromide  by  Hydrogen  Peroxide 61 

A  Possible  Method  of  Measuring  the  Strengths  of  Acids 62 

Are  the  Ions  Factors  in  the  Absorption  of  Light  ? 62 

The  Oxidization  of  Uranous  Salts  by  Nitric  Acid 64 

Uranous  Acetate  and  the  Effect  of  the  Addition  of  Nitric  Acid 65 

The  Selective  Action  of  Chemical  Reagents  on  Solvates 66 

The  Reduction  of  Uranyl  Salts  in  Solution 69 

Reduction  of  Uranyl  Chloride  in  Methyl  Ester 69 

Selective  Reduction  of  Uranyl  Aggregates 70 

Direct  Spectroscopic  Evidence  for  the  Effect  of  Mass 71 

CHAPTER  V.     THE  EFFECT  OF  TEMPERATURE  ON  ABSORPTION  SPECTRA: 

Solvates  and  the  Effect  of  Change  in  Temperature  on  the  Relative  Intensity  of 

Solvate  Bands 74 

Neodymium  Chloride  in  Water  and  Ethyl  Alcohol 77 

Neodymium  Bromide  in  Water  and  Methyl  Alcohol 77 

Neodymium  Chloride,  Bromide,  and  Nitrate  in  Water 77 

Neodymium  Chloride  in  Methyl  Alcohol 78 

Neodymium  Bromide  in  Methyl  Alcohol 79 

Neodymium  Nitrate  in  Isobutyl  Alcohol 79 

Neodymium  Nitrate  in  Acetone 80 

Erbium  Chloride  in  Water 80 

Uranyl  Chloride  in  Acetone 81 

Uranyl  Nitrate  in  Propyl  Alcohol 81 

Uranyl  Chloride  and  Nitrate  in  Isobutyl  Alcohol 81 

Uranyl  Chloride  and  Nitrate  in  Methyl  Ester 81 

Uranous  Chloride  in  Water  and  Methyl  Alcohol 82 

Uranous  Chloride  in  Acetone 82 

The  Existence  of  Aggregates  and  Their  Properties,  and  the  Effect  of  Rise  in  Tem- 
perature on  the  Aggregates 83 

Neodymium  Salts  in  Acid  Solutions 84 

Uranous  Sulphate  in  Sulphuric  Acid 85 

Uranyl  Nitrate  in  Nitric  Acid,  Uranyl  Chloride  in  Hydrochloric  Acid,  and 

Uranyl  Sulphate  in  Sulphuric  Acid 86 

CHAPTER  VI.     SUMMARY    AND    GENERAL    DISCUSSION: 

Mapping  of  Spectra 87 

A  Theory  of  Absorption  Spectra 89 

Solvation 92 

The  Uranyl  and  Uranous  Bands 94 

Aggregates  and  Their  Properties 95 

The  Effect  of  Temperature  on  Absorption  Spectra 98 

DESCRIPTION  OF  PLATES 101 

INDEX .102 


CHAPTER  I. 

THE  ABSORPTION  AND  EMISSION  CENTERS  OF  LIGHT 
AND  HEAT. 

During  the  last  decade  a  considerable  number  of  physicists  have  directed 
their  efforts  towards  solving  some  of  the  many  problems  of  spectroscopy.  The 
following  chapter  will  contain  a  discussion  of  some  of  this  work,  with  the  view 
of  recording  part  of  our  experimental  knowledge  concerning  the  nature  of  the 
emission  and  absorption  centers  of  light;  the  connection  between  these  centers 
and  molecular  and  atomic  structures;  the  effect  of  ionization  and  recombina- 
tion on  these  centers,  and  the  effects  and  changes  that  can  be  produced  by 
physical  and  chemical  agents  such  as  temperature,  the  presence  of  a  mag- 
netic field,  etc.,  upon  the  constitution  of  the  emission  and  absorption  centers. 

Emission  and  absorption  centers  will  be  defined  as  the  smallest  particles 
from  which  we  can  obtain  characteristic  absorption  or  emission  spectra.  A 
further  division  of  the  centers  of  any  characteristic  spectrum  would  make  it 
impossible  to  obtain  that  spectrum,  though  the  resultant  particles  may  possess 
characteristic  absorption  or  emission  spectra  of  their  own.  When  emission 
or  absorption  centers  move  with  reference  to  an  observer,  the  frequencies  of 
the  spectral  lines  and  bands  will  show  the  Doppler  effect. 

ATOMIC  STRUCTURE  AND  SPECTRA. 

A  very  important  problem  is  that  of  the  relation  between  chemical  con- 
stitution and  absorption  or  emission  spectra,  although  the  relation  between 
flame,  spark,  and  arc  spectra,  and  the  chemistry  of  the  absorption  and  emission 
centers  may  not  be  known.  Even  the  source  of  spectra  like  that  from  the  blue 
cone  of  a  bunsen  burner,  the  Swan  spectra,  is  at  present  a  much  mooted  ques- 
tion. It  is  probable  that  chemical  reactions  play  an  important  role  in  emis- 
sion and  absorption  spectra,  and  especially  in  band  spectra.  We  usually  think 
of  most  spectrum  lines,  like  DI  and  D2  of  sodium,  as  coming  from  the  metallic 
atoms.  Fredenhagen  points  out  that  under  most  conditions  oxygen  is  present. 
In  chlorine,  hydrogen,  or  fluorine  flames,  calcium,  strontium,  thallium,  sodium, 
barium,  and  copper  emit  spectra  that  are  very  different  from  those  obtained 
when  oxygen  is  present.  Under  these  conditions  thallium  does  not  emit  the 
characteristic  green  line,  and  the  lines  DI  and  D2  are  completely  absent.  Work 
on  the  absorption  of  sodium,  mercury,  potassium,  and  various  other  vapors 
shows  that  the  presence  of  foreign  gases  modifies  the  character  of  the  absorp- 
tion very  much. 

Chemical  reactions  and  processes  of  ionization  and  recombination  are 
believed  to  place  the  atom  or  molecule  in  a  peculiar  condition,  in  which  it 
can  emit  energy  to  the  ether  or  absorb  energy  from  it.  Under  ordinary  con- 
ditions the  atom  does  not  seem  capable  of  doing  this.  In  sodium  vapor,  for 
instance,  according  to  present  theories  only  one  atom  in  thousands  is  taking 
part  in  absorption  at  any  one  time.  The  problem  as  to  how  energy  is  trans- 
1  1 


2  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

ferred  to  and  from  matter  is  one  of  the  most  fundamental  problems  of  science. 
A  striking  example  of  the  fact  that  a  few  atoms  under  peculiar  conditions  have 
the  power  of  absorbing  an  enormous  amount  of  energy  is  exhibited  by  the  iron 
absorption  lines  in  the  solar  spectrum.  An  arc  of  carbon  electrodes  containing 
iron  as  an  impurity  emits  enough  iron  vapor  to  absorb  as  much  as  the  iron 
vapor  in  the  sun.  It  is  thus  seen  that  an  infinitesimal  amount  of  iron  in  the 
very  great  atmosphere  of  the  sun  is  sufficient  to  absorb  a  large  part  of  the 
energy  emitted  by  the  photosphere. 

Our  present  theory  of  the  mechanism  of  the  absorption  and  emission  of 
radiations  is  very  simple.  Light  and  heat  are  electromagnetic  radiations,  and 
hence  the  emission  and  absorption  centers  must  contain  either  or  both  electric 
charges  and  magnetic  poles.  As  free  magnetic  poles  are  unknown  to  us,  while 
free  electric  charges  are  known,  this  theory  makes  the  electric  charge  the  origin 
of  electromagnetic  phenomena.  At  present  no  positive  electric  charges  are 
known  to  be  associated  with  portions  of  matter  smaller  than  the  hydrogen 
atom.  On  the  other  hand,  negative  electrons  are  known  to  be  associated  with 
masses  only  about  one  two-thousandth  that  of  the  hydrogen  atom.  As  far  as 
experiment  shows,  these  electrons  always  have  the  same  properties  and  the 
same  charge  (the  charge  is  invariably  considered  as  constant  when  e/m  varies), 
no  matter  from  what  element  they  may  come.  It  is  for  these  reasons  that  the 
electron  is  made  the  fundamental  unit  in  the  electromagnetic  theory.1 

Electromagnetic  radiations,  then,  have  their  origin  in  electric  charges. 
Continuous  spectra  (as  from  hot  metals)  are  due  to  free  electrons,  and  these 
apparently  have  very  little  connection  with  the  chemical  constitution  of  the 
metal  molecules.  Fine  line  and  band  spectra  are  apparently  due  to  different 
systems  of  electrons  within  the  atom,  and  are  greatly  affected  in  intensity 
by  the  presence  of  neighboring  atoms.  The  electrons  of  this  type  vibrate  in 
definite  frequencies  that  can  be  changed  only  very  slightly  by  changing  the 
external  conditions. 

THE  IONIZATION  THEORY  AND  ABSORPTION  AND  EMISSION  CENTERS. 

Several  investigators  have  considered  that  band  spectra  are  due  to  vibra- 
tions in  some  way  peculiar  to  a  condition  existing  during  the  dissociation  of  mole- 
cules or  the  recombination  of  the  dissociated  parts.  According  to  Koenigs- 
berger  and  Ktipferer  the  band  spectra  of  iodine,  bromine,  nitrogen  dioxide, 
sulphur,  iodine  trichloride,  and  probably  nitrogen  and  the  other  gases  are  due 
to  a  dissociation  of  this  kind.  Iodine  is  a  typical  example.  At  60°  C.  and 
about  4  mm.  pressure  the  reaction,  as  expressed  by  them,  is  as  follows: 


At  about  800°  C.  this  reaction  is  practically  complete.  According  to  them, 
iodine  possesses  a  continuous  absorption  which  has  a  maximum  in  the  green, 
and  this  continuous  absorption  decreases  with  rising  temperature.  At  600° 
and  above,  the  absorption  is  almost  entirely  in  the  violet  and  ultra-violet  and 
is  due  to  the  iodine  atom.  The  banded  absorption,  consisting  of  thousands  of 
fine  lines,  results  whenever  chemical  reactions  represented  by  the  above  equa- 

1  Phys.  Zeit.,  8,  729  (1907).  2  Ibid.,  II,  568  (1910). 


ABSORPTION    AND    EMISSION    CENTERS. 


tion  take  place.  During  these  reactions  it  is  possible  that  the  atoms  may  exist 
in  the  so-called  "nascent"  condition,  and  their  electrons  may  then  be  subjected 
to  very  little,  if  any,  damping.  In  such  reactions  it  might  be  expected  that 
the  gas  would  be  greatly  ionized.  This,  however,  is  not  the  case,  as  was  shown 
by  Henry1  and  Whiddington.2 

Several  workers,  including  Galitzin  and  Wilip,3  have  studied  the  absorp- 
tion spectra  of  bromine  at  different  temperatures  and  pressures.  As  the  tem- 
perature is  raised  the  fine  band  absorption  spectrum  changes,  becomes  more  and 
more  indistinct,  and  finally  disappears  at  high  temperatures.  Evans4  has 
shown  that  the  temperature  of  the  disappearance  of  the  absorption  bands  is 
higher  the  greater  the  pressure.  The  disappearance  of  the  absorption  lines 
is  closely  connected  with  the  dissociation  of  the  diatomic  bromine  molecules, 
and  the  disappearance  of  absorption  at  high  temperatures  can  be  explained 
by  assuming  that  the  monatomic  molecules  have  no  absorption  between  X  3500 
and  X  6800. 

Heated  bromine  and  iodine  vapors  give  an  emission  spectrum  that  coin- 
cides with  the  absorption  banded  spectrum.  Evans  believes  that  the  absorp- 
tion spectra  disappear  as  soon  as  the  emission  due  to  the  dissociation  and 
recombination  of  the  diatomic  molecules  is  equal  to  the  absorption  of  the 
undissociated  state.  Evans  gives  the  following  table: 


Pressure  of 
bromine 
vapor. 

Temperature 
of  disappear- 
ance of 
spectrum. 

Fraction  of 
dissociation. 

Fraction  of 
dissociation 
observed  by 
spectroscope. 

mm. 

°C 

24 

950 

0.22 

0.25 

35 

1030 

.37 

.39 

49 

1090 

.49 

.51 

63 

1136 

.58 

.58 

88 

1220 

.74 

.68 

160 

1320 

.84 

.79 

246 

0) 

(*) 

i  Spectrum  still  present  at  1320°  C. 

-  Tube  becomes  opaque,  collapsing  at  1400°  C. 

StTLPHtm  BANDS. 

Graham5  has  investigated  the  absorption  spectra  of  sulphur  vapor  between 
530°  and  900°  C.,  the  pressure  being  in  general  about  10  mm.  of  mercury. 
Above  580°  C.  the  dissociation  is  considered  to  be  from  S8  to  82.  At  or  below 
520°  C.,  Graham  believes  that  there  are  intermediate  compounds  formed 
between  S8  and  S2.  The  following  are  the  wave-lengths  of  some  of  the  sul- 
phur bands: 

1  Proc.  Camb.  Phil.  Soc.,  9,  319  (1897). 

2  Ibid.,  15,  189  (1909). 

3  M&noires  de  TAcactemie  des  Sciences  de  St.-Petersbourg,  17,  1-112  (1906). 
«  Astrophys.  Journ.,  32,  281  (1910). 

5  Proc.  Roy.  Soc.,  A,  84,  311  (1910). 


THE    ABSORPTION    SPECTRA    OF   SOLUTIONS. 


Ss                     Sj 

4775 

4245  : 

3415 

3060 

2805 

4705 

4195 

3365 

3025    2770 

4645    4150 

3330 

2990    2745 

4580    4100 

3290 

2960 

2715 

4530 

4050 

3255 

2930 

2690 

4465 

4005 

3215 

2900 

2665 

4405 

3985 

3170 

2860 

2640 

4350 

3130 

2835 

2620 

1  •_".)() 

3095 

The  question  as  to  whether  the  fluorescence  of  a  gas  or  liquid  influences 
its  conductivity  has  in  general  been  answered  in  the  negative.  Nichols  and 
Merritt1  reported  that  the  conductivity  of  an  alcoholic  solution  of  eosin  was 
increased  when  the  solution  was  caused  to  fluoresce.  Carmichel2  and  Regner3 
found  no  such  effect,  while  Hodge4  and  Goldman5  have  shown  that  the  effect 
found  by  Nichols  and  Merritt  was  due  to  an  electromotive  force  produced 
by  the  light  at  the  electrodes  of  the  cell.  Howe8  finds  that  if  the  fluorescence 
of  anthracene  increases  the  conductivity,  the  increase  is  too  small  to  measure. 
Wood  could  detect  no  increase  in  the  conductivity  of  sodium  vapor  when  it 
was  caused  to  fluoresce. 

On  the  other  hand,  Nichols  and  Merritt7  believe  that  in  the  case  of  the 
fluorescence  of  solutions  of  fluorescein,  the  emission  center  may  be  the  ion, 
although  they  have  examined  the  effect  of  change  of  concentration  upon  the 
absorption  spectrum  of  eosin  and  find  very  little  effect.  The  absorption  curve 
is  steep  towards  the  red,  and  gradual  towards  the  violet.  The  fluorescent 
curve  slopes  in  the  opposite  manner.  Their  work  indicates  that  the  molecules 
and  ions  seem  to  behave  in  much  the  same  way  in  absorption  phenomena. 
The  same  writers8  have  investigated  the  problem  as  to  whether  the  fluorescence 
excited  per  unit  of  absorbed  energy  is  constant  for  all  wave-lengths.  Confin- 
ing the  range  of  absorption  to  that  of  a  single  band,  they  conclude  that  the 
light  near  the  red  side  of  the  band  is  more  effective  in  producing  fluorescence 
than  that  lying  on  the  violet  side;  and  the  change  in  specific  exciting  power 
in  passing  along  the  band  is  continuous,  without  any  indication  of  anything 
selective  in  the  neighborhood  of  the  region  of  maximum  absorption. 

THE  CARRIERS  OF  CANAL-RAY  SPECTRA. 

A  large  number  of  investigations  have  been  made  on  the  spectra  produced 
by  canal  rays.  In  the  earlier  work  Stark  was  of  the  opinion  that  the  renewal 
of  energy  to  a  vibrating  atom  took  place  at  the  moment  of  collision  between 
the  radiating  atom  and  some  other  moving  part;  and  the  smaller  the  mass  of 
the  particle  collided  with,  the  more  efficient  it  would  be  in  exciting  vibrations 
inside  the  atom,  since  the  velocity  of  the  small  particle  is  greater  and  the  time 
occupied  by  a  collision  would  be  shorter.  Continuous  radiation  of  energy  by 
an  atom  moving  with  a  comparatively  small  velocity  would  only  be  made 


1  Phys.  Rev.,  19,  296  (1904). 

2  Jour,  de  Phys.,  4,  873  (1905). 

3  Phys.  Zeit.,  4,  862  (1903). 

4  Ibid.,  28,  25  (1908). 


5  Ann.  d.  Phys.,  27,  332  (1908). 
1  Phys.  Rev.,  30,  453  (1910). 
''Ibid.,  31,  376  (1910). 
8  Ibid.,  381  (1910). 


ABSORPTION    AND    EMISSION    CENTERS.  5 

possible,  then,  by  its  frequent  collisions  with  free  electrons.  On  the  other 
hand,  band  spectra,  which  are  not  in  general  affected  by  electric  fields,  Stark 
considers  as  being  due  to  the  combining  of  a  positive  ion  and  a  negative 
electron.  During  this  recombination  there  is  a  considerable  decrease  in  the 
potential  energy  of  the  system,  and  it  is  from  this  energy  that  the  band  spec- 
trum is  produced. 

In  their  early  work  Stark  and  Riecke1  describe  an  arc-like  discharge 
between  copper  electrodes  of  about  3600  volts  difference  in  potential.  The 
vapors  of  sodium  or  lithium  salts  placed  in  this  discharge  spread  towards 
the  negative  wire,  thus  indicating  that  the  carriers  are  positive;  this  being 
a  direct  contradiction  of  Lenard's  results. 

Most  of  Stark's  later  work  has  been  done  with  canal  rays.  They  move 
towards  the  cathode  and  pass  through  any  openings  in  it,  with  a  velocity  of 
about  108  cm.  per  second.  If  there  is  hydrogen  in  the  tube  both  the  line  and 
band  spectra  of  hydrogen  may  be  seen.  In  nitrogen  the  line  spectra  are  diffi- 
cult to  obtain.  The  lines  of  hydrogen,  nitrogen,  mercury,  sodium,  potassium, 
etc.,  are  found  to  show  the  Doppler  effect  when  viewed  in  the  direction  in 
which  the  canal-ray  particles  are  moving. 

The  substances  showing  the  Doppler  effect  also  give  spectra  that  do  not 
show  the  Doppler  effect,  i.e.,  there  are  rest  lines  and  shifted  lines.  The  rest 
line  is  usually  much  the  sharper  of  the  two,  and  the  space  between  the  two 
lines  is  usually  dark.  The  line  shifted  towards  the  violet  usually  has  its  sharp- 
est side  on  the  red.  The  rest  line  comes  largely  from  the  gas  through  which 
the  canal  rays  are  passing.  The  displaced  line  is  composed  of  light  radiated 
by  the  canal-ray  particles  themselves,  and  since  these  lines  are  hazy,  the  canal 
rays  are  moving  with  different  velocities,  according  to  the  part  of  the  "cathode 
fall"  region  from  which  the  particles  originate.  The  particles  that  traverse 
the  whole  region  of  the  cathode  fall  will  accordingly  have  the  maximum  veloc- 
ity. Having  passed  through  a  field  of  from  300  to  500  volts,  the  velocity  of 
the  canal-ray  particles  becomes  sufficient  to  produce  ionization  by  collision. 

Knowing  the  cathode  fall,  the  mass  of  the  canal  particle,  and  the  maxi- 
mum displacement,  Stark  calculates  the  charge  of  the  canal  particle.  For  the 
hydrogen  series,  the  principal  and  subordinate  series  of  sodium  and  potas- 
sium, and  for  certain  lines  of  mercury,  the  value  of  the  charge,  according  to 
the  earlier  papers  of  Stark,  is  the  same  as  that  of  the  elementary  charge  of 
electricity.  Stark  also  considered  the  mercury  triplets  to  be  due  to  particles 
carrying  a  double  charge,  and  the  mercury  line  X  4078.1  to  be  due  to  a  carrier 
having  more  than  two  charges. 

THE  CARRIERS  OF  SPARK  SPECTRA. 

Among  investigators  who  have  taken  up  the  problem  as  to  what  is  the 
nature  and  velocity  of  the  particles  in  sparks  that  are  acting  as  absorption  and 
emission  centers  of  line  spectra,  may  be  included  Schuster  and  Hemsalech,2 
Schenck,3  Royds,4  Milner,5  Miss  Schaeffer,6  and  others.  These  workers  have 

1  Phys.  /oil..  5,  :.:;7  (1<>()4). 

2  Phil.  Trans.,  193,  209  (1900);  Compt.  Rend.,  142,  1511  (1906). 

3  Astrophys.  Journ.,  14,  116  (1901). 
«  Phil.  Trans.,  208.  A,  333  (1908). 
57faY/.,  209,  71  (1908). 

8  Astrophys.  Journ.,  28,  121  (1908). 


D  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

studied  the  velocity  of  the  light  streamers,  and  in  some  instances  have  found 
indications  that  the  emitting  centers  carried  a  negative  charge.  The  subject  is 
such  a  complicated  one,  however,  that  it  must  be  stated  that  our  knowledge  at 
present  concerning  the  constitution  of  these  emission  centers  is  extremely 
meager. 

THE  EMISSION   CENTERS  OF   FLAMES  AND  ARCS. 

The  study  of  the  Zeeman  effect  has  shown  beyond  a  doubt  that  the  vibra- 
tions of  the  emitting  centers  of  many  arc,  spark,  and  flame  lines  are  affected 
by  an  outside  magnetic  field,  in  the  same  way  as  negative  electrons  would  be 
affected;  and  it  is  remarkable  how  closely  the  value  of  e/m,  as  calculated  from 
the  Zeeman  effect,  agrees  with  the  value  as  found  for  the  cathode  and  /3-ray 
particles.  The  Zeeman  effect  does  not,  however,  give  us  much  knowledge  of 
the  radiating  centers,  since  the  electrons  form  only  a  small  part  of  these  centers. 

A  very  important  series  of  experiments  has  been  carried  out  by  Lenard1 
and  others.  The  main  conclusion  from  this  work  was  that  the  carriers  of  the 
first  subordinate  series  in  the  Kayser  and  Runge  classification  of  spectrum 
lines  are  positively  charged  ions.  The  reason  that  ions  in  liquids  do  not  radi- 
ate, Lenard  explains  as  due  to  their  being  loaded  down  by  neutral  molecules. 
The  work  of  other  investigators  has  made  this  conclusion  very  doubtful,  so 
that,  as  in  the  case  of  spark  and  canal-ray  spectra,  it  must  be  concluded  that 
at  present  nothing  is  known  with  certainty  as  to  what  the  constitution  of  the 
radiating  centers  may  be. 

SCHUMANN  WAVES. 

In  1893  Schumann  studied  the  extremely  short  ultra-violet  wave-lengths 
to  about  X  1200.  Lyman2,  by  using  a  concave  grating,  has  studied  the  spectra  of 
hydrogen  from  X  2000  to  X  1030,  there  being  no  radiations  apparently  between 
X  3000  and  X  1700.  Argon  possesses  a  rich  emission  spectrum  in  this  region. 
The  spectra  of  carbon  monoxide  and  dioxide  seem  to  be  very  much  alike,  and 
produce  radiations  to  X  1300.  Oxygen  and  nitrogen  do  not  seem  to  emit  in 
this  region.  Fluorite  is  the  only  substance  transparent  to  X  1225.  Quartz 
0.5  mm.  thick  absorbs  everything  beyond  X  1500.  Argon,  helium,  hydrogen, 
and  nitrogen  in  a  layer  of  1  cm.  are  perfectly  transparent.  The  absorption  of 
air  is  due  to  the  presence  of  oxygen.  Oxygen  of  9  mm.  depth  and  380  mm. 
of  mercury  pressure  has  an  absorption  band  extending  from  X 1750  to  X 1275. 

THE  POSSIBLE  CATALYTIC  ACTION  OF  LIGHT. 

Weigert3  has  worked  upon  the  equilibrium  of  the  gas  COCk  and  its 
products,  CO+C12.  The  reaction 

CO  +  C12->COC12 

is  accelerated  by  the  action  of  light,  but  the  position  of  the  final  equilibrium  is 
unaffected  by  the  action  of  the  light,  and  is  a  function  only  of  the  temperature. 
The  light  thus  acts  as  a  catalyzer  and  not  as  a  source  of  energy. 

'Ann.  d.  Phys..  9,  642  (1902):  11,  649  (1903):  12,  475  (1903);  12,  737  (1903);  17, 
197  (1905). 

*Ibid.,  77,777  (1907). 

sLe  Radium,  4,  373  (1907);  Ann.  d.  Phys..  24,  243  (1907). 


ABSORPTION    AND    EMISSION    CENTERS.  7 

Weigert  believes  that  there  are  formed  molecular  complexes  or  "reaction 
nuclei"  by  the  light,  analogous  to  the  ions  formed  by  ultra-violet  light  in  air; 
and  these  "reaction  nuclei"  play  the  role  of  a  catalyzer,  the  reaction  being 
produced  with  very  great  velocity  on  the  surfaces  of  these  nuclei,  and  the  speed 
of  the  reaction  will  then  be  a  function  of  the  rate  of  diffusion  of  these  nuclei. 

Weigert  finds  that  these  "reaction  nuclei"  act  as  nuclei  for  the  conden- 
sation, and  thus  supports  the  views  of  Burgess  and  Chapman.1  When  the 
light  has  produced  a  number  of  the  "reaction  nuclei,"  it  is  found  that  the 
number  of  these  decay  like  ordinary  ions.  The  "reaction  nuclei"  also  accel- 
erate the  following  reactions: 

(1)  Dissociation  of  oxy chloride  of  carbon. 

(2)  Oxidization  of  hydrogen. 

(3)  Oxidization  of  sulphurous  acid. 

(4)  Decomposition  of  ozone. 

(5)  Oxidization  of  hydrochloric  acid  gas. 

(6)  Formation  of  ammonia. 

EMISSION  SPECTRA  OF  ORGANIC  COMPOUNDS. 

Goldstein2  has  shown  that  bright,  fluorescent,  and  phosphorescent  light 
is  emitted  by  solid  aromatic  compounds.  The  stimulation  is  best  produced  by 
cathode-ray  bombardment.  To  prevent  the  evaporation  of  the  compounds, 
they  are  kept  cooled  by  liquid  air.  Goldstein  has  investigated  a  large  number 
of  organic  compounds  such  as  benzene,  the  three  xylenes,  benzonitrile,  the 
quinolines,  acetophenone,  etc.  In  many  cases  three  spectra  appear  which 
Goldstein  calls  the  initial,  the  chief,  and  the  solution  spectra. 

During  the  first  moments  of  excitation  the  initial  emission  spectrum  is 
quite  strong,  but  it  soon  becomes  very  weak  without  disappearing.  At  the 
same  time  that  the  initial  spectrum  begins  to  diminish  in  intensity  the  chief 
spectrum  appears.  This  spectrum  is  a  very  characteristic  one,  even  for  iso- 
meric  compounds.  The  third  type  of  spectra  only  appears  when  an  aromatic 
compound  is  dissolved  in  a  liquid  and  the  solidified  solution  is  exposed  to 
cathode  rays. 

The  chief  spectrum  consists  largely  of  narrow  channeled  bands,  which 
usually  have  their  sharper  edges  on  the  short  wave-length  side.  These  spectra 
never  have  bands  of  shorter  wave-length  than  X  4600.  The  initial  spectra 
extend  much  farther  than  this  into  the  region  of  short  waves. 

CHIEF  SPECTRUM  OF  NAPHTHALENE. 
/  5390  (very  bright)         5890  (very  bright) 
5550  6150  (probably  double) 

5600  6300 

5730  6480 

SPECTRUM  OF  NAPHTHALENE  IN  MONOCHLORBENZENE. 

A  4730  bright         5050         5170  faint         5400  faint         5570  faint         5820  faint 
4830      "  5100         5230     "  5450     "  5650     ' 

The  solution  spectrum  varies  greatly  for  different  solvents,  even  for 
isomeric  compounds. 

1  Trans,  (hem.  Sue.,  89,  1423  (1906). 

2  Verhandl.  d.  deutsch.  Ges.,  vi,  156,  185  (1904);  Phil.  Mag.,  20,  619  (1910). 


8  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

The  phosphorescence  of  several  organic  compounds  has  been  studied  by 
Kowalski.1  Phosphorescence  was  found  to  appear  in  many  cases  at  about 
—  150°  C.,  depending  on  the  substance  dissolved  in  the  alcohol.  When  phos- 
phorescence first  appears  it  only  lasts  a  few  hundredths  of  a  second,  but  as 
the  temperature  is  lowered  the  duration  of  the  phosphorescent  light  increases 
very  appreciably.  If  the  time  of  excitation  is  short,  an  "instantaneous"  phos- 
phorescence results  which  resembles  the  fluorescence  of  the  solution.  If  the 
time  of  excitation  is  increased,  fine  bands  are  superimposed  upon  the  broad 
fluorescent  bands,  and  these  increase  in  intensity  as  the  time  of  excitation  is 
increased.  The  time  required  to  reach  a  maximum  intensity  is  different  for 
different  bands.  The  duration  of  these  bands  is  much  longer  than  that  of  the 
"instantaneous"  phosphorescence,  and  is  called  by  Kowalski  "progressive 
phosphorescence . ' ' 

Kowalski  and  Dzierzbicki  give  the  following  wave-lengths  for  the  pro- 
gressive phosphorescent  bands  in  ethyl  alcohol: 

(1)  Benzene,  0.05  normal  solution  in  alcohol:  XX  3390,  3460,  3520,  3570, 
3650,  3710,  3800,  3850,  3970,  4020,  4130,  4190,  4290,  4350. 

(2)  Toluene,  ethylbenzene,  and   propylbenzene,  0.05   normal   solution 
in  alcohol.    The  introduction  of  the  methyl  group  into  the  benzene  nucleus 
transforms  the  14  benzene  doublets  into  7  broad  bands,  occupying  almost  the 
same  position  in  the  spectrum.    An  introduction  of  a  methyl  group  in  a 
side  chain  produces  very  little  effect.    The  toluene  bands  are  at  XX  3460,  3580, 
3650,  3800,  3890,  4060,  and  4120.    The  ethylbenzene  bands  are  at  XX  3450, 
3580,  3640,  3780;  3870,  4050,  and  4120.     The  propylbenzene  bands  are  at 
XX  3440,  3580,  3650,  3790,  3890,  4050,  and  4130. 

(3)  The  bands  of  a  0.05  normal  solution  of  o-xylene,  C6H4(CH3)2,  are  at 
XX  3480,  3560,  3610,  3670,  3780,  3830,  3900,  4000,  4070,  and  4130;  m-xylene, 
C6H4(CH3)2,  at  3540,  3610,  3670,  3730,  3820,  3880,  3970,  4090,  4160,  and  4230; 
and  p-xylene,  C6H4(CH3)2,  at  3550,  3650,  3700,  3770,  3890,  3950,  4010,  4120, 
4190,  and  4270. 

(4)  Pseudocumene,  mesitylene,  and  cymene  all  show  bands  at  XX  3560, 
3650,  3770,  3880,  4000,  4120,  and  4270. 

(5)  Phenol  shows  bands  at  XX  3510,  3610,  3710,  3830,  3960,  and  4080. 

(6)  o-cresole  has  bands  at  XX  3530,  3630,  3740,  3850,  and  3970;  m-cresole 
at  3540,  3620,  3730,  3850,  3970,  and  4080;  p-cresole  at  3630,  3730,  3850,  3980, 
and  4110. 

THE  ABSORPTION  SPECTRA  OF  ORGANIC  COMPOUNDS. 

THE  UNIT  OF  THIS  ABSORPTION. 

In  discussions  concerning  the  color  of  organic  compounds  it  is  customary 
to  speak  of  the  selective  absorption  as  being  due  to  certain  ions  or  molecules. 
This  is  probably  true  in  the  infra-red,  the  electric  charges  absorbing  these  long 
wave-length  radiations  being  probably  associated  with  masses  of  molecular 
size.  However,  in  the  visible  and  ultra-violet  portions  of  the  spectrum  the 
value  e/m  of  the  absorbers  is  invariably  of  the  same  magnitude  as  that  of  the 
electron.  Drude2  has  investigated  a  large  number  of  organic  compounds, 

1  Compt.  Rend.,  151,  810  (1910). 

2  Ann.  d.  Phys.,  14,  677,  726,  936,  961  (1904). 


ABSORPTION    AND    EMISSION    CENTERS.  9 

and  shows  that  the  absorber  of  all  the  shorter  waves  of  the  spectrum  is  the 
negative  electron. 

Throughout  this  part  of  the  present  monograph  the  absorbers  are  con- 
sidered as  negative  electrons.  These  electrons  have  certain  free  periods  cor- 
responding to  the  bands  of  selective  absorption.  These  free  periods  are  greatly 
modified  by  the  presence  of  certain  chemical  radicals,  and  seem  to  be  elec- 
trons that  are  situated  either  in  the  outer  parts  of  the  atom  or  between  two 
or  more  atoms.  Stark  and  others  call  these  the  valency  electrons,  and  con- 
sider that  chemical  valency  is  due  to  them.  Chemical  bonds  will  then  be 
closely  associated  with  the  electric  fields  of  these  electrons.  While  the  theory 
in  its  present  state  is  confronted  with  many  difficulties,  yet  it  seems  a  step 
towards  the  explanation  of  the  more  or  less  vague  chemical  bond.  As  an  aid 
to  our  imagination,  we  shall  consider  atoms  or  ions  as  large  spherical  regions 
throughout  which  a  positive  charge  is  uniformly  distributed.  These  regions 
are  sometimes  spoken  of  as  "spheres  of  influence."  Two  atoms  collide  when 
their  "spheres  of  influence"  touch.  Groups  of  atoms  composing  ions,  radicals, 
or  molecules  will  have  "spheres  of  influence."  No  ion  can  penetrate  the 
sphere  of  influence  of  another  atom  or  molecule.  On  the  other  hand,  the  elec- 
trons are  very  small  and  bear  much  the  same  relations  in  size  to  the  atom 
that  the  sun  bears  to  the  solar  system.  The  electric  fields  of  the  electrons, 
however,  occupy  quite  large  volumes,  although  the  energy  of  this  field  is  for 
the  most  part  situated  in  a  very  small  space.  Electrons  can,  therefore,  move 
through  ions  and  atoms  if  they  have  sufficient  velocity.  In  most  organic  com- 
pounds it  is  considered  that  the  valency  electrons  move  in  the  interatomic 
spaces  with  considerable  ease.  In  the  metals  a  large  number  of  the  electrons 
are  free.  In  organic  compounds  that  are  transparent  to  certain  wave-lengths, 
the  electrons  in  general  will  be  held  within  certain  regions  by  forces  that  are 
supposed  to  be  elastic  in  their  nature. 

A  considerable  amount  of  work  has  been  done  by  Koenigsberger  and 
Kichling1  on  the  determination  of  the  coefficients  of  absorption  of  organic 
coloring  matters,  compounds  of  the  metalloids,  minerals,  etc.  Selective 
absorption  is  classified  under  two  heads.  In  the  first  class  the  absorbing  and 
reflecting  powers  are  closely  connected,  and  the  absorption  is  probably  due  to 
electrons  or  ions  vibrating  in  the  chemical  molecule;  in  the  second  class  the 
absorption  has  no  effect  on  the  reflecting  power,  and  the  absorbers  in  this  case 
are  rare  and  are  not  connected  with  the  molecular  structure. 

Letting  p  be  the  number  of  electrons  per  molecule,  it  is  found  that  absorp- 
tion curves  give  the  value  of  p  e/m  better  than  the  dispersion  curves.  For 
organic  coloring  matters  p  e/w=1.3(10)7.  For  a  temperature  of  absolute 
zero,  they  consider  that  p  e/w  =  1.78(10)7.  This  quantity  decreases  as  the 
temperature  rises  to  the  probable  limit  ^  1.78(10)7.  For  the  metalloids  there 
is  a  single  vibrating  electron  for  the  bromine  family  of  elements,  two  for  the 
selenium  family,  and  three  for  the  phosphorus  family. 

For  a  large  number  of  substances,  the  absorption  curve  is  displaced  towards 
the  red  when  the  temperature  is  raised.  It  widens  and  becomes  flatter  at  the 
same  time.  From  this  it  seems  that  the  quasi-elastic  force  that  acts  on  the 
electron  decreases  with  rise  in  temperature. 

1  Ann.  d.  Phys.,  28,  cS89  (1909);  32,  843  (1910);  Phys.  Zeit.,  12,  1  (1911). 


10  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

THE  THEORY  OF  CHROMOPHORES. 

In  considering  absorption  spectra  it  is  often  quite  sufficient  to  speak  qual- 
itatively of  the  color  of  different  compounds.  The  introduction  of  certain 
groups  into  colorless  compounds  often  results  in  a  colored  compound.  Any 
such  group  is  a  chromophore.  Sometimes  the  chromophore  may  be  weak,  and 
it  may  require  the  addition  of  several  chromophores  to  produce  a  colored  com- 
pound. Ultimately  the  color  is  due  to  absorbers  existing  in  the  chromophore, 
probably  the  valency  electrons.  Among  the  better  known  chromophores  are 
the  groups: 

>C  =  C<  =CO  >C  =  NH,          —  CH-N—          —  N  =  N— 

-^C—  N—  N—  ,N—  .0  /O 

\/  -7C—  NC  —  N=0  —  N^  —  N/  j 

O  X)  ^O  XO 


The  ethylene  group,  >C  =  C<,  is  a  weak  chromophore,  and  several 
chromophores  must  be  present  before  the  absorption  is  sufficient  to  produce 
color.  An  example  is  that  of  benzene  and  its  isomer  : 

CH=CH—  CH          CH=CH 


Benzene  is  colorless  and  exhibits  absorption  only  in  the  ultra-violet, 
whereas  the  isomeric  compound  is  orange  yellow. 

The  carbonyl  group,  =C  =  0,  is  also  weak,  and  several  of  the  groups 
must  be  present  in  a  compound  to  produce  color.  The  following  examples 
indicate  how  an  increasing  number  of  the  carbonyl  groups  produces  a  greater 
and  greater  absorption  of  the  shorter  wave-lengths  : 

R—  CO—  R,  colorless. 
CH3—  CO—  CO—  CH3,  yellow. 
C6H5—  CO—  CO—  C6H5,  yellow. 
CH3—  CO—  CO—  CO—  CH3,  orange. 
C6H5—  CO—  CO—  CO—  CO—  C6H5,  red. 

The  combination  of  two  phenyl  groups  causes  absorption  only  in  the 
ultra-violet.  The  introduction  of  the  —  CH  =  N  —  chromophore  is  sufficient 
to  produce  color,  as  is  shown  in  the  yellow  benzylidenaniline,  Cf)H5CH  = 
N  —  C6H5.  The  azochromophore,  —  N  =  N  —  ,  produces  the  same  effect,  as 
shown  in  the  orange  azobenzene,  C6H5  —  N  =  N  —  C6H5.  The  chromophores 

v  \  *&— 

-^C  —  N  —  N  —  and  —  ^C  —  Nf          ,  on  the  other  hand,  are  very  weak. 


O 

The  nitroso  group,  —  N  =  O,  is  a  very  strong  chromophore  when  it  is 
joined  to  a  carbon  atom  directly.    The  effect  of  this  chromophore  is  shown  in 


ABSORPTION    AND    EMISSION    CENTERS.  11 

nitrosobenzene,  ON — C,}H5,  which  is  green.    Wallach,1  and  recently  J.  Schmidt,2 
have  investigated  the  following  compounds,  which  are  of  a  deep  blue  color: 

CH3— CH— C(CH3)2  CH3— CH— C(CH3)2 

NO     O— NO  NO     6— NO, 

Alkylenenitrosite.  Alkylenenitrosate. 

According  to  Wolff,3  the  following  nitroso  compounds,  the  first  of  which 
is  green  and  the  second  blue,  have  the  structures: 


ON— C— C— CH, 


N 


X 


CH3—  C—  N—  C6H5  CH3—  C—  NH 

l-phenyl-3.5-dimethyl-4-  3-5-dimethyl-4- 

nitrosopyrazol.  nitrosopyrazol. 

The  carrier  of  the  color  in  these  cases  is  the  C  —  N  =  O  group.  Many  of 
the  aliphatic  nitroso  compounds  show  polymerization  and  are  then  often  col- 
orless. The  polymerization  of  R  —  N  =  O  to  (RNO)2  is  probably  accompanied 
by  a  rearrangement  as  follows: 

/°\ 
R—  N<         N—  R. 


This  would  explain  why  the  polymer  is  colorless. 

An  application  of  the  theory  of  isodynamic  isomerism  has  been  made  by 
K.  Schaefer4  to  the  absorption  of  the  NO3  group.  An  exhaustive  study  has 
been  made  of  the  absorption  of  alkyl  and  metallic  nitrates.  In  every  nitrate 
investigated,  the  characteristic  ultra-violet  absorption  was  detected,  and  in 
general  Beer's  law  was  found  to  hold.  It  would  be  interesting  to  know  whether 
the  presence  of  other  salts,  acids,  or  solvents  would  change  the  N03  absorption. 
Schaefer  finds  for  pure  neutral  solutions  of  inorganic  salts  that  the  absorption 
is  independent  of  the  metal.  The  absorption  band  appears  to  be  independ- 
ent of  the  ionization,  since  in  the  case  of  potassium  nitrate  the  absorption 
is  the  same  for  the  solid  as  for  the  concentrated  and  dilute  aqueous  solutions. 
The  absorption  is  suggested  to  be  due  to  the  following  oscillation: 


The  character  of  the  absorption  is  similar  for  metallic  and  many  organic 
salts.  Methyl,  ethyl,  amyl,  and  allyl  nitrates,  however,  show  only  general 
absorption.  There  was  no  evidence  here  of  selective  absorption,  either  in 
the  liquid,  vapor,  or  dissolved  condition  of  the  salts. 


1  Lieb.  Ann.,  241,  288  (1887);  322,  305  (1902). 

2  Ber.  d.  chem.  CJes.,  35,  2323,  3721  (1902);  36,  1768  (1903). 

3  Lieb.  Ann.,  325,  192  (1902). 

•Zeit.  wiss.  Phot,,  8,  212-234  and  237-287  (1910). 


12 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


The  nitro  group  — NC       or  — N\  |     is  a  very   weak   chromophore. 

^0  XO 

The  aliphatic  nitro  compounds,  CH3NO2,  C2H5N02,  etc.,  are  colorless.  When 
combined  with  other  chromophores,  colored  compounds,  such  as  nitroben- 
zene or  nitronaphthalene,  can  be  obtained.  Stobbe1  has  investigated  the 
influence  of  the  nitro  group  on  the  fulgides.  In  solution  the  p-nitrophenyl- 
fulgide  has  a  deep  red  color.  The  ortho  and  meta  compounds  are  much  less 
deeply  colored. 

Hantzsch2  and  Raschig3  have  shown  that  the  =N  =O  group  acts  as  a 
chromophore  in  the  sulphonate,  O  =  N  =  (SO3K)2,  which  is  violet  in  solution 
and  orange  in  the  solid  state.  The  thiocarbonyl  group,  =C  =  S,  is  a  rather 
strong  chromophore.  Examples  are  the  blue  compounds  thioacetophenone, 
C6H5— CS— CH3,  and  thiobenzophenone,  C6H5— CS— C6H5.  For  a  fuller 
account  of  the  color  properties  of  various  compounds,  the  reader  is  referred 
to  Ley's  paper,4  from  which  the  data  here  recorded  have  been  largely  taken. 

There  has  been  a  great  deal  of  discussion  whether  quinone  has  the  for- 
mula I  or  II: 


II. 

Willstsitter  and  F.  Mtiller5  have  found  that  o-benzoquinone  can  exist  in 
two  forms,  I  and  II,  the  former  being  colorless  and  the  latter  red : 


\ 


— o 

J, 


j  =  0 
i  =  0 


II. 


This  fact  may  possibly  explain  several  outstanding  difficulties  among 
quinone  derivatives.  It  would  be  expected  that  the  substitution  of  an  (NR) 
group  for  oxygen  in  a  quinone  would  give  a  deeply  colored  substance.  As  a 
matter  of  fact,  quinonediphenylimide, 

NC6H5 


1  Ber.  d.  chem.  Ges.,  38,  4082  (1905). 

2  Ibid.,  28,  2744(1895). 

3  Dammer:  Handb.  d.  anorg.  Chem. 

4  Jahrb.  d.  Rad.  u.  Elek.,  6,  274-381  (1909). 

5  Ber.  d.  chem.  Ges.,  41,  2580  (1908). 


ABSORPTION    AND    EMISSION    CENTERS. 


13 


is  brownish  red.  But  the  compounds  NH  :  C6H4  :  NH  and  0  :  C6H4  :  NH  are 
colorless.  This  can  easily  be  explained  if  the  latter  compounds  are  assumed 
to  have  the  superoxide  formula  similar  to  that  of  o-benzoquinone.  The  qui- 
none  chromophore  enters  into  the  composition  of  quite  a  large  number  of 
colored  compounds. 

The  space  relations  of  the  chromophores  seem  to  affect  the  color  of 
compounds.  For  instance,  the  ethylene  group  can  have  two  isomeric  config- 
urations : 

It  — C — -H  R — C — H 


This  geometric  isomerism  may  explain  the  following  facts: 

1.  Diethoxynaphthostilbenes,  C2H50 — C10H6.CH    :    CH.C^Hg.OC-jHj.1 
The  form  which  has  the  highest  melting-point  is  colorless,  while  the  lower 
melting  form  is  yellow. 

2.  Dibenzoylethylenes,  C6H5CO.CH  :  CH.COC6H5.2    The  higher  melt- 
ing form  is  colorless,  while  the  lower  melting  form  possesses  a  deep  yellow 
color. 

That  the  color-producing  power  of  the  chromophores  is  due  to  the  double 
bonds  seems  quite  certain.  When  these  bonds  are  saturated  the  resulting 
compounds  are  colorless. 

Colored.  Colorless. 

C6HS.  CO.  CO.  CO.  C6HS,  diphenyltriketone.  C6HS.  CO.  CH2.  CO.  C6H5,  dibenzoylmethane. 

C6H5— N  =  N— CSH5,  azobenzene.  C6H5NH— NHC,H6,  hydrazobenzene. 

C6H8 — N  =  O,  nitrosobenzene.  C6H5 — N.  H.  OH,  phenylhydroxylamine. 

O  =  C6H4  =  O,  quinone.  HO .  C6H4 .  OH,  hydroquinone. 

The  different  di-  and  tri-substitution  products  usually  give  rise  to  dif- 
ferent absorption  bands  when  the  absorption  is  selective.  Ortho-  and  meta- 
xylene  have  one  band,  whereas  paraxylene  has  two.  The  following  gives  the 
value  of  the  limit  of  absorption  when  light  is  passed  through  a  gram  molecule 
of  the  substance : 


Cresol. 

1 

Dihydroxy- 
benzene. 

Hydroxy- 
benzoic  acid. 

Meta 

3433 

3466 

3359 

Ortho.  .  .  . 

!       3413 

3399 

3080 

Para  

3359 

3151 

2986 

When  a  chromophore  is  introduced  into  a  compound  the  bands  may  be 
shifted  towards  the  red  or  towards  the  violet.  The  former  effect  is  batho- 
chromous,  the  latter  hypsochromous.  The  effect  of  joining  chromophores  is 
usually  bathochromous.  For  example: 


A 

A 

A 

A 

Benzene  .  .  . 

2610    2540    2450 

2440 

Naphthalene  
1  Anthracene  

2850 

2720 
3600 

2630 
3430 

2550 
3280 

1 

Elbs:  Journ.  prakt.  Chem.,  47,  72  (1893). 

Paal  and  Schulze:  Ber.  d.  chem.  Ges.,  33,  3795  (1900);  35,  168  (1902). 


11 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


In  triphenylmethane  the  limit  of  the  visible  portion  of  the  spectrum 
is  reached.  It  may  be  stated  that  anthracene  and  phenanthrene  have 
entirely  different  absorption  spectra,  although  the  fluorescent  spectra  are  very 
similar.1  An  auxochrome  is  a  radical  that  causes  the  absorption  to  be  more 
intense.  An  example  is  —  CO  —  C  =  C  —  CO  —  ,  which  appears  in  the  indigos, 


C.H 


, 
C0H4 


and  also  in  the  deeply  colored  compounds 

/cox      -,/co\ 

\^4\        /C  =  C\         /C6H4  C6H4<^ 


CftH4<;        )C  =  C/        \C6H4 

\o/       xo/ 


o 


The  groups  CH3,  OCH3,  C2H5,  the  halogens,  etc.,  are  bathochromes,  while 
the  groups  N02  and  NH2  are  hypsochromes. 

The  infra-red  absorption  spectra  to  about  15/j.  of  a  large  number  of  organic 
compounds  have  been  investigated  by  Julius2  and  by  Coblentz.3  Isomeric 
compounds  are  found  to  possess  very  different  absorption,  depending  on  the 
combinations  of  the  atoms  in  the  molecule.  Stereomeric  compounds,  on  the 
other  hand,  were  found  to  possess  the  same  absorption  spectra.  The  replac- 
ing of  hydrogen  by  an  NH2  or  CH3  group  usually  results  in  the  appearance 
of  new  bands.  In  the  spectrum  of  certain  benzene  derivatives,  however,  the 
benzene  spectrum  is  usually  present.  The  carbohydrates  investigated  had 
characteristic  spectra  with  absorption  bands  at  0.83  to  0.86ju;  1.67  to  1.72/t; 
3.25  to  3.43/x;  6.75  to  6.86ju;  and  13.6  to  14/1.  The  three  isomeric  xylenes  have 
banded  spectra  in  which  the  most  important  line  in  each  group  lies  farthest 
toward  the  long  wave-lengths  in  the  order  ortho,  meta,  and  para. 

Considerable  work  has  recently  been  done  by  Weniger4  upon  the  absorp- 
tion of  organic  compounds  in  the  infra-red.  He  finds  that  the  alcohols  have 
bands  at  3.0  and  6.9/i;  that  changes  from  the  primary  to  the  iso-compounds 
cause  small  shifts;  and  that  the  secondary  alcohols  have  a  band  at  7.6/1  and 
the  tertiary  alcohols  a  corresponding  one  at  7.9/t.  The  band  9.6/t  in  the  pri- 
mary alcohols  is  shifted  to  9.1/t  in  the  secondary  alcohols  and  8.6/t  in  the  ter- 
tiary alcohols.  There  are  two  minor  bands  in  the  primary  alcohols  which 
appear  as  follows: 


Methyl. 

Ethyl. 

Propyl. 

Butyl. 

3.0^ 

3.0 

3.0 

3.0 

3.5 

3.5 

4.9 

5.2 

5.5 

5.6 

5.9 

6.0                  6.1 

6.1 

9.9 

9.6                  9.6 

9.6 

10.6 

10.4 

10.4 

13.3 

13.0 

13.0 

13.0 

1  Elston:  Astrophys.  Journ.,  25,  3  (1907). 

2  Verb.  Konikl.  Akad.,  Amsterdam,  1,  No.  1  (1892). 

3  Investigations  of  Infra-red  Spectra,  Carnegie  Institution  of  Washington  Publication 
No.  35,  by  W.^W.  Coblentz. 

4  Phys.  Rev.,  31,  408  (1910). 


ABSORPTION    AND    EMISSION    CENTERS.  15 

It  is  seen  that  the  shifts  are  towards  the  9/x  region  of  the  spectrum.    For 
the  secondary  alcohols  Weniger  gives  the  following: 


Propyl. 

Butyl. 

Capryl. 

7.2 

7.3 

7.3 

9.0 

9.1 

9.1 

9.9 

9.8 

9.4 

In  the  case  of  primary  acids  Coblentz  and  Weniger  give  the  positions  of 
the  following  minima: 


Acetic 

3 

fyt 

. 

q 

7  2 

8  9 

9  9 

10  6 

11  0 

13  9 

Butyric  
Valeric  
Caproic  
Stearic  
Cerotic 

2 
.'.'.'.       5' 
3. 
....      3. 
3 

6 
6 
5 
5 
5 

5 
5 
5 

.', 

.9 
9 
.9 

q 

7.1 
7.1 
7.0 
7.0 
6  9 

7.9 

7.9 
8.0 

7.8 

7  7 

9.3 
9.1 
9.1 

9.2 

10.6 
10.7 
10.8 
10.6 
10  6 

12.9 
12.2 
11.6 
12.2 
10  9 

13^3 
12.5 
13.3 
I9  9 

Weniger  considers  the  3.0  and  6.9w*  bands  in  the  alcohols  to  be  related  to  the 
hydroxyl  group;  the  3 AH  band  in  the  alcohol,  acids,  and  esters  to  be  related  to 
methylene  (CH2);  the  7.3/i  band  in  the  esters  and  higher  alcohols  to  be  also 
related  to  methylene;  and  the  bands  o.9ju  and  8.2^  in  all  substances  for  which 
there  are  data  to  carbon  monoxide. 

The  9.6yu  band  in  the  primary  alcohols  shifts  by  O.OM  to  the  violet  when  the 
linking  of  the  hydroxyl  is  changed  to  secondary,  and  O.S/z  further  changes 
when  the  tertiary  alcohol  is  formed.  The  change  from  the  primary  to  the 
secondary  linking  of  the  carboxyl  group  (CH2COOH  to  CHCOOH)  causes 
the  doubling  of  a  band  in  the  8/z  region,  this  being  true  for  acids  and  esters. 
The  band  of  the  carbonyl  group  is  independent  of  the  way  in  which  this 
group  is  linked. 

The  authors1  have  shown  that  the  effect  of  the  NO3  group  and  of  free 
nitric  acid  is  hypsochromous,  causing  the  uranyl  bands  to  shift  towards  the 
violet.  The  effect  of  free  hydrochloric  acid  or  of  zinc,  aluminium,  or  calcium 
chlorides  on  the  uranyl  chloride  bands  is  bathochromous.  Recently  the 
authors  have  found  that  the  NO3  group  is  hypsochromous  with  respect  to  the 
neodymium  and  erbium  bands. 

IXFL/UENCE    OF   THE    SOLVENT. 

Theoretically  it  would  be  expected  that  the  position  of  the  absorption 
bands  would  be  different  for  different  solvents.  Kundt's  rule  that  the  bands 
should  be  shifted  to  the  red  as  the  refractive  index  increases  does  not  hold. 
It  is  usually  believed  that  the  application  of  Kundt's  rule  is  obscured  by  the 
formation  of  compounds  between  the  dissolved  compound  and  the  solvent. 
The  formation  of  such  solvates  seems  to  be  quite  definitely  proved  for  some 
inorganic  compounds  and  organic  solvents.2  Kauffman,  Hantzsch  and  Glover, 
Gorke,  Koppe  and  Staiger,  and  others,  have  recently  shown  that  the  extinc- 

1  Phys.  Rev.,  28, 143,  29,  555  (1909) ;  30,  279  (1910). 

2  Anderson:  Phys.  Rev.,  26,  520  (1908).    Jones  and  Strong:  Phys. Zeit.,  10, 499  (1909); 
Amer.  Chem.  Journ.,  43,  37,  97  (1910). 


If, 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


tion  coefficient  varies  somewhat  for  every  solvent.  In  the  same  solvent  the 
extinction  coefficient  usually  increases  as  radicals  are  added  to  the  dissolved 
substance,  increasing  its  molecular  weight.  Hantzsch1  furnishes  evidence 
which  shows  the  presence  of  solvates  and  molecular  aggregates  in  the  case  of 
nitrohydroquinone  dimethyl  ether. 

An  interesting  investigation  has  been  made  by  Kalandek.2  Resonators 
will  emit  electromagnetic  waves  of  different  wave-lengths,  depending  on  the 
index  of  refraction  of  the  liquid  in  which  they  are  vibrating.  Kalandek  inves- 
tigated the  effect  of  different  solvents  on  the  period  of  various  resonators, 
and  also  on  the  positions  of  the  absorption  bands  of  a  large  number  of  organic 
compounds.  In  general,  the  relations  were  not  very  close.  It  would  be  very 
interesting,  however,  to  carry  these  investigations  into  the  infra-red. 

THE  ABSORPTION  SPECTRA  OF  BENZENE  AND  ITS  DERIVATIVES. 

Benzene  and  several  of  its  derivatives  show  selective  absorption  in  the 
ultra-violet.  Generally  the  absorption  spectra  of  organic  compounds  consist 
of  very  wide,  diffuse  bands.  The  absorption  bands  of  gaseous  benzene,  on  the 
other  hand,  are  very  fine.  Benzene  in  solution  shows  seven  absorption  bands 
between  X  2330  and  X  2710,  and  in  the  gaseous  state  about  30  bands.  Pauer,3 
Friedrichs,4  Grebe,5  and  Hartley6  have  investigated  several  of  the  benzene 
compounds.  The  bands  in  the  gaseous  state  are  much  finer  and  usually  more 
numerous  than  in  solution  or  in  the  solid  state. 

Both  the  vapor  and  solution  bands  are  shifted  to  the  red  when  Cl,  Br, 
CH3,  etc.,  are  substituted  for  hydrogen.  The  shift  is  generally  greater  the 
greater  the  molecular  weight  of  the  radical.  The  bands  of  benzene  shifted  in 
this  way  are  the  ones  that  are  common  to  benzene,  toluene,  ethylbenzene, 
and  hydroxyxylene,  and  are  unaffected  by  temperature  and  pressure.  Hartley 
gives  the  following  wave-lengths  for  benzene: 


A 

A 

A 

A 

A 

* 

A 

In  solution  
As  vapor  

2682 
2670 

2657-2642 
2630 

2614-2600 
2590 

2539 
2523 

2480 
2466 

2426.5 
2411 

2376 
2360 

As  far  as  investigated,  the  substitution  products  of  benzene  have  much  less 
characteristic  spectra  than  the  spectrum  of  benzene  itself.    It  would  be  very 
interesting  to  know  whether  the  shift  of  the  bands  is  gradual  as  the  state  is 
changed  or  as  different  radicals  are  added. 
Anthracene  has  the  following  bands: 


A 

A 

A 

A 

A 

Solid  

4250 

4495 

4745 

4980 

5300 

Solution  

4050 

4275 

4540 

4820 

(Fluorescent)  vapor 

3900 

4150 

4320 

1  Ber.  d.  chem.  Ges.,  40,  1556  (1907). 

2  Phys.  Zeit,  9,  128  (1908). 

3  Wied.  Ann.,  61,  363  (1897). 
4Z.  wiss.  Phot.,  3,  154  (1905). 
'Ibid.,  3,  363  (1905). 

•  Journ.  Chem.  Soc.,  77,  839  (1900).     Phil.  Trans.,  208,  A,  475-528  (1908). 


ABSORPTION    AND    EMISSION    CENTERS. 


17 


The  substitution  of  saturated  groups  in  benzene  has  been  found  to  change 
the  absorption  spectra  but  little.  Unsaturated  radicals  like  NH2,  COOH,  etc., 
change  the  spectra  very  greatly,  so  that  there  is  hardly  any  relation  to  the 
benzene  spectra.  In  the  various  di-substitution  products,  the  para  com- 
pounds retain  the  characteristics  of  the  benzene  absorption  better  than  the 
ortho  or  meta  compounds.  A  considerable  amount  of  work  has  been  done  by 
Hartley,1  Baly  and  Desch,2  Ley  and  von  Engelhardt,3  Baly  and  Collie,4  Ley,5 
Hartley  and  Hedley,8  Baly  and  Tuck;7  and  others  have  worked  on  the  halogen, 
amino,  and  nitro  compounds  of  benzene,  the  phenols,  pyridine,  and  its  substi- 
tution products.  Below  are  a  few  of  the  results  obtained. 

Purvis8  has  studied  the  absorption  spectra  of  the  vapors  of  pyridine  and 
some  of  its  derivatives  at  different  temperatures  and  pressures.  Following  are 
some  of  the  bands: 


Pyridine. 

Pyridine. 

Pyridine.      n-Picoline. 

Piperidine. 

Piperidine. 

2930  n.  wk. 

2815  dif. 

2747  wk.   2880  wk.  sh. 

2637  wk. 

2535  St. 

2918  n.  wk. 

2809  dif. 

2743  wk.   2861  wk. 

2633  wk. 

2530  st. 

2913  n.  wk. 

2806  wk. 

2738  wk.   2859  wk. 

2628  wk. 

2528  wk. 

2895  n.  wk. 

2798  wk.  n. 

2736  wk.   2856  wk. 

2625  wk. 

2526  wk. 

2892  n.  wk. 

2796  wk. 

2733  wk.  j  2846  wk. 

2599  wk. 

2521  wk. 

2878  sh.  wk. 

2795  wk. 

2730  st.    2834  wk. 

2596  wk. 

2519  st. 

2869  sh.  wk. 

2789  st. 

2726  st. 

2821  wk. 

2595  wk. 

2513  st. 

2866  sh.  wk. 

2784  wk.  n. 

2718  st.    2819  wk. 

2591  wk. 

2507  st. 

2861  sh.  wk. 

2782  wk.  n. 

2713  st.    2814  wd. 

2590  wk. 

2503  st. 

2859  sh.  wk. 

2778  wk.  n. 

2696  dif.    2809  wd. 

2589  wk. 

2502  wk. 

2855  wk. 

2762  wk.  n. 

2690  dif.    2790  n. 

2586  wk. 

2499  wk. 

2849  wk. 

2760  wk.  n. 

2685  dif. 

2786  wd. 

2579  sh. 

2495  wk. 

2843  wk. 

2758  wk.  n. 

2678  wk. 

2785  wd. 

2565  wd. 

2490  wk. 

2832  sh.  st. 

2754  st. 

2673  wk. 

2781  wd. 

2558  wd. 

2472  wk. 

2822  sh.  wk. 

2552  wk. 

2467  wk. 

2550  wk. 

2461  wd. 

2547  wk. 

2455  wd. 

2543  wk. 

2450  wd. 

2539  wk. 

n.=narrow;  wk.  =  weak;  sh.=sharp;  st.=strong;  dif.  =diffuse;  wd.  =  wide. 

In  the  pyridine  vapor  spectrum  it  was  found  that  the  longer  wave-length 
bands  became  wider  and  increased  in  intensity  as  the  temperature  and  pres- 
sure were  increased.  In  fact,  all  bands  showed  an  increase  in  width  and  inten- 
sity under  these  conditions,  and  the  general  absorption  in  the  ultra-violet  was 
also  greatly  increased.  The  piperidine  bands  are  wider  and  more  diffuse  than 
the  pyridine  bands.  Some  of  the  piperidine  bands  were  coincident  with  the 
benzene  bands.  Benzene  bands,  however,  have  most  of  the  sharp  edges  of  the 
bands  on  the  red  side,  whereas  the  piperidine  bands  are  wider  and  are  diffuse 
on  both  sides. 

Hartley  has  shown  that  the  vapors  of  o-,  ra-,  and  p-xylenes,  l-methyl-4- 
propylbenzene,  and  1  :  3  :  5-trimethylbenzene  have  very  few  bands  compared 
with  benzene  vapor,  which  has  82  bands.  The  same  is  true  of  pyridine  vapor, 
in  comparison  with  the  much  smaller  number  of  bands  of  a-picoline  and  the 


1  Handbuch  der  Spectroscopie,  vol.  HI. 

2  Journ.  Chem.  Soc.,  93,  1345,  1747,  1902  (1908). 

3  Ber.  d.  chem.  Ges.,  41,  2990  (1908). 

4  Journ.  Chem.  Soc.,  87,  1344  (1905). 

2 


s  Her.  d.  chem.  Ges.,  41,  1637  (1908). 
•  Journ.  Chem.  Soc.,  91,  319  (1907). 
1  Ibid.,  93,  1902  (1908). 
8  Journ.  Chem.  Soc.,  97,  692  (1 


IS 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


disappearance  of  the  bands  in  the  lutidines  and  trimethylpyridine.  The  dis- 
appearance of  the  bands  as  the  number  of  methyl  groups  in  the  pyridine  ring 
increases  is  analogous  to  the  lessened  persistency  of  the  absorption  band  as 
the  number  of  methyl  groups  is  increased  when  the  substances  are  examined 
in  alcoholic  solution.  No  absorption  bands  are  found  for  alcoholic  solutions  of 
piperidine. 


VAPORS. 

Furane. 

Furfuraldehyde. 

Thiophene. 

2652  weak. 

2726  weak. 

2681 

2590  weak. 

2647  " 

2725   " 

2679 

2530  " 

2642  " 

2720   " 

2676  weak.   2500  weak,  wide. 

2637  " 

2718   " 

2674  weak,  i  2416  about  0.5  A.  U. 

wide. 

2634  strong. 
2630  weak. 

2712  strong. 
2709   " 

2668       2406  about  0.7  A.  U. 
2666       2395  wide. 

wide. 

2627  wide. 

2706  weak. 

2660 

2620  " 

2704   " 

2654 

2601  weak. 

2701   " 

2652 

2599  " 

2699   " 

2641 

2593  " 

2697   " 

2639 

2589  head  of  strong  band. 

2688  strong. 

2541  weak. 

2538  " 

2530  head  of  strong  band. 

Alcoholic  solutions  of  furane,  thiophene,  and  pyrrol  show  no  bands 
according  to  Purvis.1  Neither  do  the  liquids  furfuraldehyde,  thiophene,  or 
pyrrol  have  any  absorption  bands. 

THEORY  OF  DYNAMIC  ISOMERISM. 

Baly,  Stewart,  Desch,  and  others  have  recently  supported  the  view  that 
the  absorption  of  light  by  organic  compounds  does  not  take  place  under  ordi- 
nary conditions,  but  only  when  there  is  a  change  in  the  union  of  the  atoms.  In 
some  cases  this  change  of  union  takes  place  when  a  chemical  compound 
changes  into  an  isomeric  form.  Dynamic  isomerism  exists  when  there  is 
some  third  substance  to  act  as  an  intermediary.  Many  substances  are  iso- 
dynamic  only  at  high  temperatures  or  in  the  presence  of  a  catalytic  agent. 
Sometimes  the  solvent  may  promote  isomeric  change.  The  point  of  equilib- 
rium is  determined  by  the  velocities  of  the  isomeric  change,  and  these  veloc- 
ities are  affected  by  the  solvent,  concentration,  temperature,  catalytic  reagent, 
or  the  presence  of  free  alkalis  or  acids. 

An  example  of  the  above  change  is  the  transfer  of  a  labile  hydrogen  atom 
from  an  oxygen  or  sulphur  atom  to  a  carbon  or  nitrogen  atom.  Sometimes 
an  OH  or  CN  group  is  transferred  in  the  same  way.  The  atom  or  radical 
transferred  assumes  a  neutral  condition  compared  with  its  condition  as  a 
powerful  negative  radical  in  the  inorganic  acids. 

The  theory  of  dynamic  isomerism  is  useful  in  explaining  a  large  number 
of  phenomena  in  organic  chemistry,  and  especially  those  connected  with 


1  Journ.  Chem.  Soc.,  98,  1648  (1910). 


ABSORPTION    AND    EMISSION    CENTERS.  19 

light  emission  and  absorption.  Tschugaeff1  has  examined  some  five  hundred 
compounds  for  triboluminescence  (luminescence  due  to  the  crushing  of  the 
compound)  and  has  found  that  25  per  cent  of  the  organic  compounds  inves- 
tigated showed  a  more  or  less  intense  flash  when  crushed.  Most  of  the  lumin- 
escent compounds  could  have  existed  in  several  isodynamic  forms.  Phos- 
phorescence and  fluorescence  may  be  explained  as  being  due  to  a  dynamic 
isomerism  existing  between  two  or  more  forms.  For  instance,  fluorescein 
may  exist  in  two  or  more  forms: 

O  O 


NOH          HO/  X)H 

/\    /     ^     \    A    /\    / 


c 

C6H4COOH 


CO 


We  shall  now  consider  some  recent  work  by  Baly  and  Desch.  They  first 
took  up  acetylacetone,  CH3— CO— CH2 — CO — CH3,  and  ethyl  acetacetate, 
CH3— CO— CH2— CO2C2H5,  and  their  metallic  derivatives.  Acetylacetone 
and  its  metal  derivatives  were  found  to  give  similar  spectra.  Ethyl  acetace- 
tate was  found  to  give  only  a  very  slight  general  absorption,  whereas  its  alu- 
minium derivative  gave  a  spectrum  almost  exactly  like  that  of  acetylacetone. 
The  work  of  Perkin  and  others  has  shown  that  free  acetylacetone  is  enolic 
and  ethyl  acetacetate  ketonic. 

H    OH  O 

CH3— CO— C  =  C— CH3 

H 

Acetylacetone  (enolic).  Ethyl  acetacetate  (ketonic). 

These  results  would  then  indicate  that  the  metallic  derivatives  of  ethyl 
acetacetate  have  the  enolic  structure,  the  metal  taking  the  place  of  hydrogen 
in  the  OH  group.    But  by  using  various  compounds  it  was  shown  that  neither 
H 

I 
the  ketonic  group,  — C — C — ,  nor  the  enolic  group,  — CH  =  C — ,  gives  rise  to  a 

H  ok 

trace  of  banded  absorption.    This  would  also  result  from  Hartley's  work. 

It  would  seem  probable,  then,  that  the  absorption  was  not  to  be  attrib- 
uted to  any  definite  molecular  structure,  but  to  a  dynamic  isomerism  exist- 
ing between  the  two  modifications  of  the  compound  in  solution.  It  was  stated 
before  that  alkalis  and  acids  change  the  velocity  of  the  transformation  from 

1  Ber.  d.  chem.  Ges.,  34,  1820  (1901). 


20  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

one  form  to  the  other,  the  final  state  being  unaffected  by  the  catalytic  agent. 
This  latter  condition  means  that  the  direct  and  reverse  actions  are  equally 
changed.  If  now  intra-molecular  change  is  the  source  of  the  absorption 
bands,  then  a  catalytic  agent  should  affect  the  persistence  of  the  band.  Experi- 
mental results  verified  these  conclusions.  Other  compounds  were  tried  with 
similar  results. 

From  these  results  it  follows  that  there  must  exist,  in  connection  with 
the  reversible  transformation  of  one  tautomeric  form  into  the  other,  a  system 
that  is  synchronous  with  the  light  absorbed.  This  can  not  be  a  vibration  of 
the  labile  atom  itself,  since  the  oscillation  frequency  of  the  absorption  bands 
does  not  bear  any  direct  relation  to  the  mass  of  the  labile  atom,  and  the  fre- 
quency of  atomic  motions  is  never  so  high  as  these.  The  absorption  must  be 
due,  however,  to  the  oscillation  of  linking  of  the  keto-enol  tautomers: 

H 

— CH  =  C—  <=>  — C— C— ,  or,  symbolically,  — CH— C— 
OH  II    O  O* 

where  the  asterisks  indicate  the  points  where  the  migrations  of  linkages  occur. 
From  a  summary  of  work  previously  done  on  ultra-violet  absorption  spectra, 
it  was  seen  that  most  of  the  compounds  showing  absorption  also  were  tau- 
tomeric. As  was  also  seen,  an  increase  in  the  mass  of  the  molecule  in  general 
decreased  the  oscillation  frequency  of  the  absorbed  light,  although  by  only  a 
small  amount. 

Assuming  the  saturnian  form  of  atom  similar  to  the  arrangement  assumed 
by  Sir  J.  J.  Thomson,  chemical  bonds  would  simply  consist  of  Faraday  tubes 
of  force.  By  a  rearrangement  of  Faraday  tubes,  it  is  quite  probable  that 
a  vibrational  disturbance  would  be  set  up.  If  Hewitt's  explanation  of  the 
origin  of  fluorescence  is  correct,  it  would  follow  that  disturbances  set  up  by 
isodynamic  changes  are  of  the  same  frequency  as  light  waves.  The  lumin- 
osity due  to  thermal  or  electric  action  is  caused  by  rapid  changes  of  stress 
or  of  the  electric  action  to  which  the  atoms  are  subjected.  Here  the  disturb- 
ances of  the  electrons  are  due  to  the  oscillation  of  linkages  within  the  mole- 
cule. The  comparatively  small  displacement  of  the  absorption  band  by  a 
change  in  the  mass  of  the  molecule  is  to  be  expected,  since  an  increase  in  the 
mass  of  matter  near  a  vibrating  electron  has  the  effect  of  retarding  its  motion, 
the  oscillation  frequency  becoming  less.  For  instance,  the  spectral  series  of 
Kayser  for  various  related  elements  show  a  displacement  towards  the  red  on 
increasing  the  atomic  mass.  This  is  in  general  true  for  all  emission  spectra 
and  for  the  absorption  spectra  of  the  rare  earths  and  organic  dyes. 

The  sodium  and  aluminium  derivatives  of  ethyl  acetacetate  show  the 
enolic  and  ketonic  modifications  in  dynamical  equilibrium.  The  sodium  com- 
pound is  found  to  be  easily  decomposed  into  sodium  hydroxide  and  ethyl 
acetacetate,  whereas  the  aluminium  derivatives  show  dissociation  and  hydrol- 
ysis to  only  a  very  slight  extent.  The  absorption  spectrum  is  not  dependent 
on  ionization  or  hydrolysis.  Hartley  has  found  that  the  ultra-violet  absorp- 
tion spectra  of  metallic  nitrates  is  exhibited  even  on  very  great  dilution,  show- 


ABSORPTION    AND    EMISSION    CENTERS. 


21 


ing  a  close  connection  between  the  anion  and  cation  in  such  solutions.  Baly 
and  Desch  conclude  that  the  Faraday  tubes  may  be  lengthened  out  on  dilu- 
tion, and  that  the  force  necessary  for  the  separation  is  furnished  by  the  attrac- 
tion of  the  solvent.  Solvents  which  thus  exert  a  strong  attracting  force  are 
ionizing  agents;  and  this  attraction  is  exerted  both  on  molecules  and  ions. 
We  have  thus  hydrated  molecules  and  ions.  When  the  Faraday  tubes  are 
lengthened  beyond  a  certain  critical  value,  an  interchange  of  ions  between 
the  molecules  becomes  possible.  A  completely  dissociated  solution  of  a  salt 
is  not  one  in  which  the  ions  are  moving  independently  of  one  another,  but 
one  in  which  the  length  of  the  Faraday  tubes  is  greater  than  the  critical 
value.  In  tautomeric  compounds  the  Faraday  tubes  connect  the  labile  atom 
with  the  rest  of  the  molecule,  being  lengthened  out  to  such  an  extent  as  to 
allow  these  atoms  to  change  their  positions  in  the  molecule,  and  there  is  a 
sort  of  internal  ionization  within  the  molecule.  To  this  making  and  breaking 
of  Faraday  tubes  may  be  attributed  the  absorption  of  the  light. 

In  the  tautomeric  aliphatic  compounds  the  substitution  of  an  alkyl  group 
for  the  labile  atom  destroys  the  tautomerism.  This  would  be  expected,  since 
alkyl  ions  are  unknown.  Water  and  other  solvents  do  not  have  sufficient 
attractive  force  to  lengthen  out  the  Faraday  tubes  in  this  case.  Whether 
there  is  a  banded  absorption  in  these  cases  is  not  stated.  One  consequence  of 
the  theory  can  be  tested.  Since  the  persistence  of  the  absorption  band  is  a 
measure  of  the  number  of  molecules  undergoing  transformation  at  any  mo- 
ment, this  persistence  should  reach  a  limit  for  each  tautomeric  compound  when 
the  length  of  the  Faraday  tubes  has  reached  their  critical  length,  so  that  free 
interchange  takes  place.  By  the  successive  addition  of  an  accelerating  com- 
pound a  maximum  should  be  found.  Experiment  shows  this  to  be  true.  Take 
the  case  of  ethyl  benzoylsuccinate,  to  which  1,  10,  20,  and  100  equivalents  of 
sodium  hydroxide  have  been  added.  The  limits  of  persistence  referred  to  a 
0.0001  normal  solution  of  the  ester  are  as  follows: 


Free 
ester. 

NaOH. 

10  eq. 
NaOH. 

20  eq. 
NaOH. 

100  eq. 
NaOH. 

mm. 

mm. 

mm. 

mm. 

mm. 

Absorption  band  begins  at  
Absorption  band  ends  at  

120.0 

83.2 

63.0 
34.7 

40 
20 

31.7 
15.2 

21.9 
10.4 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Change  of  dilution  over  which  the 

band  persists 

30  7 

44  9 

50 

52  0 

52  5 

At  this  point  it  may  be  well  to  refer  to  the  work  of  Stewart  and  Baly. 
Quite  a  number  of  chemical  facts  have  been  explained  by  the  theory  of  steric 
hindrance,  although  this  theory  also  fails  to  explain  a  great  many  things. 
For  instance,  acetic  acid,  CH3COOH,  is  esterified  with  ease.  The  methyl, 
ethyl,  etc.,  derivatives  are  much  more  difficult  to  esterify.  This  is  explained 
as  due  to  the  larger  volumes  occupied  by  these  radicals,  and  the  consequent 
hindrance  to  the  approach  of  the  alcohol  to  the  carboxyl  radical.  If,  as  is 
probable,  however,  the  intra-molecular  mean  free  path  is  large  compared  with 
the  size  of  these  radicals,  this  explanation  in  terms  of  steric  hindrance  breaks 
down.  The  theory  of  isodynamic  change  will  explain  all  these  facts  and  also 


22  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

others  where  the  theory  of  steric  hindrance  would  lead  to  conclusions  directly 
contrary  to  the  facts.  According  to  this  theory  acetacetic  ester  exists  as 

CH3— C  =  CH— COOC2H5  <=>  CH3— C— C— H— COOC2HB 

I  II      I 

OH  OH 

During  this  dynamic  equilibrium  there  are  periods  during  which  a  nas- 
cent carbonyl  group  exists.  From  analogy  to  the  action  of  other  nascent 
substances,  this  would  occasion  a  very  much  greater  reactivity. 

Stewart  and  Baly,  on  further  investigation,  found  that  the  absorption 
band  in  this  case  has  a  persistence  which  decreases  proportionately  to  the 
decrease  of  reactivity  of  the  ketone's  carbonyl  group.  It  has  been  noticed  by 
chemists  that  the  velocity  of  tautomeric  change  depends  on  the  solvent. 
Stewart  and  Baly  also  found  that  the  persistence  of  the  absorption  band  was 
very  different  in  aqueous  and  alcoholic  solutions.  In  the  case  of  pyruvic 
ester  they  show  that  the  facts  may  be  represented  by  the  scheme 

CH3 — C — C — OC2H5  <^  CH3 — C  =  C — OC2H5 

o  o  o— o 

In  tautomerism  we  have  a  wandering  of  the  hydrogen  atom,  so  Stewart  and 
Baly  propose  to  call  this  process  isorropesis  (from  the  Greek  word  iaoppoTit-la, 
equipoise),  or  an  oscillation  in  the  carbonyl  grouping.  By  the  persistence  of 
absorption  bands  it  is  possible  to  measure  the  activity  of  chemical  compounds. 
The  band  produced  by  the  isorropesis  is  also  much  nearer  the  red  than  that 
produced  by  the  process  of  enol-keto  tautomerism.  An  example  of  isorropesis 
would  be  the  quinone  band  1/X  =  2480,  which  would  be  due  to  the  following 
change: 

O 


In  general,  then,  according  to  the  theory  of  Baly,  Desch,  Stewart,  and 
Collie,  any  absorption  by  organic  compounds  is  due  to  the  conditions  that 
occur  during  isomeric  changes.  Benzene,  for  example,  appears  in  two  forms, 
and  the  absorption  spectrum  is  due  to  a  condition  of  benzene  while  it  is  chang- 
ing from  one  form  to  the  other.  This  theory  explains  quite  well  the  action  of 
chromophores,  since,  as  we  have  seen,  every  chromophore  contains  at  least 
one  double  bond. 


ABSORPTION    AND    EMISSION    CENTERS.  23 

THEORY  OF  STARK. 

Stark1  considers  that  chemical  valency  can  be  explained  as  due  to  the 
presence  of  negative  electrons  that  hold  the  positive  parts  of  atoms  together. 
In  fig.  1  it  is  seen  how  this  can  take  place,  the  dotted  lines  representing  lines 
of  electric  force. 


FIG.  1. 

The  conditions  represented  in  fig.  1  are  such  that  there  is  very  little  stray 
electric  field  beyond  the  atoms.  Under  such  conditions  the  valency  electrons 
are  saturated  and  Stark  represents  this  by  the  symbol  < — * .  Under  many 
conditions,  however,  the  valency  electrons  are  not  so  closely  united  to  the 
atoms  and  are  more  or  less  unsaturated.  Under  certain  conditions  an  electron 
may  be  thrown  off  from  the  atom,  and  Stark  considers  that  it  is  under  some  con- 
dition such  as  this  that  selective  absorption  of  light  takes  place.  When  the  elec- 
tron returns  to  the  atom  it  will  undergo  certain  accelerations  along  its  path,  and 
during  these  accelerations  it  will  emit  radiations.  Stark  believes  that  under 
some  condition  at  least  similar  to  this,  the  fluorescent  radiation  is  emitted,  and 
that  the  period  of  this  radiation  will  depend  on  the  amount  of  energy  set  free 
when  an  electron  recombines  with  the  positive  part  H 

of  the  molecule.    From  the  heat  changes  that  occur 
in  various  chemical  reactions,  Stark  calculates  what  c 

the  approximate  period  of  these  radiations  should  ^       \^ 

be,  and  in  many  cases  obtains  values  which  agree    h 
with  the  positions  of  known  bands  in  the  spectrum. 
Among  these  bands  is  the  ultra-violet  band  of          J  { 

benzene.     Stark's  formula  for  benzene  would  be   H-<- 
the  following: 

The  symbol  — •  simply  means  that  one  elec- 
tron is  not  as  closely  joined  as  the  other  three  to 


the  carbon  atom.     It  is  possible  that  even  this  PIG   2 

unsaturated  electron  may  have  lines  of  force  run- 
ning to  the  other  carbon  atoms.    In  this  way  partial  valency  can  easily 
be  explained. 

1  Phys.  Zeit.,  9,  85  (1908). 


24  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

In  this  consideration  of  atoms  it  would  be  expected  in  general  that  the 
space  containing  the  electric  field  of  the  electron  would  more  or  less  envelop 
the  positive  nuclei  of  the  atoms,  and  that  the  volumes  of  atoms  would  depend 
on  their  valency.  This  would  agree  very  well  with  the  assumptions  of  Barlow 
and  Pope.1  These  assumptions  are  as  follows:  In  any  chemical  body  the 
relative  volumes  of  the  atoms  are  proportional  to  their  valencies;  in  a  crystal- 
lized body  the  atoms  are  close  packed;  in  a  compound  the  volumes  of  the 
spheres  of  atomic  influences  of  atoms  of  the  same  valency  may  differ  slightly. 
The  latter  variation  of  the  sizes  of  the  spheres  of  influence  (interpreted  here 
as  the  space  filled  by  the  electric  fields  of  the  valency  electrons)  may  be  due 
to  the  different  amounts  of  saturation,  or,  as  Stark  calls  it,  the  lack  of  the 
valency  electrons.  It  would  be  interesting  to  know  whether  the  energy  rela- 
tions support  this  view,  it  being  expected  that  the  greater  the  lack  of  the 
electrons,  the  less  the  potential  energy  of  the  compound. 

Stark  and  Steubing2  have  investigated  the  fluorescence  of  a  large  number 
of  organic  compounds.  Most  spectra  are  banded,  and  a  band  never  runs  in 
both  directions.  The  band  consists  of  a  tail  where  the  smaller  bands  are  close 
together.  From  the  tail  the  small  bands  may  run  towards  the  red  or  towards 
the  ultra-violet,  getting  farther  and  farther  apart  all  the  time.  But  there  are 
never  small  bands  on  both  sides  of  the  tail.  The  absorption  of  light  by  bands 
running  "to  the  red"  is  not  accompanied  by  fluorescence  or  by  any  photoelec- 
tric effects.  The  absorption  of  light  in  bands  running  towards  the  violet 
(benzene  bands)  is  accompanied  by  a  photo-electric  effect,  a  fluorescence  of 
the  bands  themselves  and  by  a  fluorescence  of  bands  due  to  the  connection  of 
carbonyl,  ethylene,  or  other  chromophoric  groups  if  these  be  present  in  the 
molecule.  The  addition  of  more  chromophores  to  the  compound  shoves 
the  fluorescent  bands  to  the  red. 

OTHER  BENZENE  THEORIES. 

There  are  some  color  changes  of  benzene  compounds  for  which  the  general 
theory  does  not  seem  easily  to  account.  For  instance,  nitronaphthalene  is 
yellow.  By  introducing  two  nitro  groups  a  colorless  compound  is  obtained. 
In  order  to  explain  phenomena  of  this  kind  Kauffmann3  assumes  that  the 
introduction  of  groups  into  a  benzene  nucleus  may  change  the  condition  of  the 
benzene  ring  itself.  He  considers  that  benzene  may  have  the  diagonal,  the 
Kelule,  or  the  Dewar4  formula. 

/\ 


\/  \ir 

I.  II.  III. 


1  Pope:  Journ.  Chem.  Soc.,  89,  1675  (1906);  91,  1150  (1907).    Swartz:  Amer.  Chem. 
Journ.,  37,  638  (1907);  42,  158  (1909). 

2  Phys.  Zeit.,  9,  481,  661  (1908). 

3  Zeit.  phys.  Chem.,  50,  530  (1905).     Ber.  d.  chem.  Ges.,  37,  2941  (1904). 

«  Ber.  d.  chem.  Ges.,  33,  1725  (1900);  34,  682  (1901);  35,  3668  (1902).     Zeit.  phys. 
Chem.,  55,  547  (1906.) 


ABSORPTION    AND    EMISSION    CENTERS.  25 

In  condition  I  benzene  has  an  aliphatic  character,  as  in  nitrobenzoic  acid, 
C6H4(NO2)COOH.  In  this  condition,  having  no  double  bonds,  it  does  not 
possess  strong  color  properties.  The  second  condition  has  an  aromatic  char- 
acter and  is  exemplified  in  the  phenols.  Examples  of  the  third  condition  are 
found  in  aniline,  p-phenylenediamine,  naphthalene,  or  anthracene.  Of  the 
three  conditions,  the  second  one  is  the  best  chromophore.  According  to  Kauff- 
mann,  benzene  vapor  exists  in  the  diagonal  condition,  and  for  that  reason  it 
is  not  luminous  when  exposed  to  electric  discharges  of  high  frequency  or  to 
the  rays  from  radium.  Auxochromes  and  chromophores  cause  the  benzene  to 
become  luminous,  and  for  this  and  other  reasons  Kauffmann  thinks  that  the 
condition  of  the  benzene  grouping  has  been  changed. 

The  different  changes  in  color  may  be  due  to  one  or  more  of  three  con- 
ditions: 

(1)  There  may  be  no  intramolecular  changes  of  constitution,  but  the 
whole  change  of  color  may  be  due  to  the  change  in  the  radicals. 

(2)  There  may  be  an  intramolecular  rearrangement. 

(3)  There  may  be  an  association  of  the  molecules  or  compounds  formed 
with  the  solvent.    The  above  classification  includes  color  changes  that  are  not 
explained  by  isomerism. 

In  many  cases  it  is  practically  impossible  to  decide  between  the  different 
possibilities.  Auwers1  and  Tuck2  give  evidence  to  show  that  the  sodium  salt 
of  hydroxyazobenzene  owes  its  color  simply  to  the  introduction  of  the  sodium. 
Baly  and  Schaefer,3  Hantzsch,4  Vey,  Gorke,5  and  others,  give  some  cases 
coming  under  class  2.  As  an  example,  we  may  take  dinitroethane : 


CH30 


Nitrophenol  ether,  faintly  yellow.  Chromonitrophenol  ether,  deep  red. 

Benzene  derivative.  Quinone  derivative. 

A  very  full  discussion  of  the  "Umlagerung"  theory  is  given  by  Ley.6  A 
short  discussion  is  also  given  of  the  theory  of  indicators,  of  polymerization, 
and  of  metallic  derivatives  of  organic  compounds,  especially  of  cases  where  the 
metal  is  supposed  to  be  present  in  the  inner  part  of  the  molecular  complex. 


1  Lieb.  Ann.,  360,  11  (1908). 

2  Journ.  Chem.  Soc.,  91,  454  (1907). 

3  Ibid.,  93,  1806(1908). 

*  Hantzsch:  Her.  d.  chem.  Ges.,  32,  575  (1899).     Hantzsch  and  Veit:  Ibid.,  33,  626 
(1900).    Ley  and  Hantzsch:  Ibid.,  39,  3149  (1906). 
5  Hantzsch  and  Gorke:  Ibid.,  39,  1073  (1906). 
9  Jahrb.  d.  Rad.  u.  Elek.,  6,  341,  381  (1909). 


CHAPTER  II. 

EXPERIMENTAL  METHODS  AND  APPARATUS. 

In  this  work  the  mapping  of  the  spectra  was  done  in  the  same  way  and 
by  the  same  methods  as  already  described  in  Publication  No.  130  of  the 
Carnegie  Institution  of  Washington,  pages  19-22.  The  general  arrangement 
of  apparatus  is  given  in  fig.  4. 

New  difficulties  that  required  special  treatment  quite  frequently  presented 
themselves  in  the  work.  As  an  example,  one  might  take  that  of  mapping  the 
absorption  spectrum  of  solutions  of  samarium,  dysprosium,  and  gadolinium 
salts,  very  kindly  lent  us  by  Professor  Urbain.  In  order  to  bring  out  as 
many  bands  as  possible,  the  absorption  cell  was  made  wedge-shaped,  the  apex 
of  the  wedge  being  about  2  mm.  wide  and  about  15  mm.  long.  In  this  way  a 
much  greater  cell  depth  could  be  obtained  with  the  same  amount  of  solution 
than  with  the  Uhler  cell.  Another  difficulty  consisted  in  getting  the  strip  of 
the  photographic  film  uniformly  exposed.  The  appearances  of  bubbles,  of 
precipitates,  etc.,  during  the  heating  of  the  solutions  are  further  examples. 
In  some  cases  these  difficulties  could  be  overcome.  For  instance,  if  the  Uhler 
cell  was  moved  back  and  forth  in  the  path  of  the  beam  of  light,  bubbles  and 
precipitates  only  decreased  the  amount  of  light  passing  through  the  solution 
and  did  not  cause  an  uneven  exposure  on  the  strip. 

Part  of  the  work  consisted  in  extending  the  Beer's  law  tests  to  very  dilute 
solutions.  Some  work  was  done  on  uranyl  solutions,  using  a  trough  with 
plane  parallel  ends.  Other  cells  consisted  of  glass  tubes  with  quartz  lenses  at 
the  ends.  One  of  these  was  500  cm.  long.  With  cells  of  this  kind  it  is  impos- 
sible to  obtain  a  uniform  exposure,  unless  the  cell  is  moved  back  and  forth  in 
the  path  of  the  beam  of  light. 

Salt  solutions  that  have  bands  in  the  violet  and  ultra-violet  were  exposed 
for  much  longer  intervals  of  time  than  those  which  have  bands  only  in  the 
visible  part  of  the  spectrum.  In  making  an  exposure  of  this  kind  (the  uranyl 
salts  are  typical  examples)  the  length  of  exposure  to  the  shorter  wave-lengths 
would  be  from  5  to  10  times  longer  than  to  the  longer  wave-lengths.  First, 
an  exposure  would  be  made  to  the  whole  spectrum  of  the  Nernst  glower;  then  a 
screen  would  be  placed  in  front  of  the  plate,  cutting  out  all  light  of  wave-length 
greater  than  about  X  4500  or  X  4800.  A  long  exposure  would  then  be  made  to 
the  short  wave-length  spectrum  of  the  glower;  and  lastly,  a  short  exposure 
would  be  made  directly  to  the  spark. 

For  high-temperature  work  on  acid  solutions  the  fused  silica  cell  was  used, 
while  for  room  temperatures  this  cell  and  the  Uhler  cell  were  used  for  such 
solutions. 

Part  of  this  investigation  consisted  in  extending  the  work  on  absorption 
spectra  to  high  temperatures,  by  means  of  closed  cells.  Two  cells,  one  1.0  cm. 
and  the  other  10  cm.  in  length,  were  used.  Fig.  3  represents  a  longitudinal 
section  of  the  longer  cell.  Since  both  cells  were  exactly  alike  in  all  respects 

27 


28 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


except  in  length  and  in  the  size  of  the  side  tube,  only  the  longer  cell  will  be 
described  here.  The  main  part  of  the  cell  (71)  was  made  of  tool  steel  and  was 
heavily  copper  plated  and  gold  plated  on  all  the  inner  surfaces. 

The  side  tube  was  very  tightly  fitted  into  the  main  part  of  the  horizontal 
tube.  The  open  part  of  the  tube  was  1.0  cm.  in  diameter.  The  windows 
of  the  cell  (U,  U)  were  2.5  cm.  in  diameter  and  were  either  of  quartz  or  glass. 
One  of  the  troubles  with  this  form  of  cell  is  the  formation  of  precipitates  on 
the  inside  surfaces  of  the  windows.  Every  time  a  precipitate  is  formed,  the 
windows  have  to  be  taken  out  and  cleaned.  On  being  put  back  there  is 
always  great  danger  of  the  quartz  or  glass  ends  being  broken.  During  the 
work  a  number  of  ends  were  broken  in  this  way. 

Quartz  ends  are  much  tougher  and  less  easily  broken  than  glass  ends. 
They  are,  however,  quite  expensive  and  in  most  of  the  work  the  solutions  were 
not  transparent  in  the  ultra-violet.  For  this  work  glass  ends  were  used.  Some 
of  these  were  cut  out  of  ordinary  plate  glass  and  others  were  made  from 


FIG.  3. 

"uviole"  glass,  which  is  tougher  and  much  more  transparent  in  the  ultra- 
violet than  the  ordinary  plate  glass.  For  cutting  the  ends  a  steel  tube  was 
fastened  to  the  axle  of  an  ordinary  fan  motor.  The  steel  tube  was  2.5  cm.  in 
diameter  and  the  motor  was  placed  so  that  the  tube  was  vertical,  the  free  end 
of  the  steel  tube  being  at  the  bottom.  An  old  glass  end  was  then  cemented  to 
a  piece  of  plate  glass  with  hot  sealing  wax  and  served  as  a  guide  for  the  steel 
tube.  The  plate  glass  was  then  held  against  the  end  of  the  steel  tube  and  the 
motor  started.  Wet  carborundum  was  fed  constantly  against  the  grinding 
steel  tube.  Plates  nearly  1.0  cm.  thick  could  be  cut  in  this  way  in  20  or  30 
minutes. 

The  quartz  windows  rested  on  gold  washers,  and  these  rested  directly 
against  the  gold-plated  shoulders  of  the  tube  T.  PPP  are  plungers.  Two 
of  these  at  the  ends  of  the  main  tube  have  guide  pins  that  prevent  the  plungers 
from  turning.  Between  the  plungers  and  the  windows  were  placed  washers. 
Various  kinds  of  washers  of  hard  leather,  lead,  zinc,  etc.,  were  used.  The 


EXPERIMENTAL    METHODS    AND    APPARATUS. 


29 


leather  washers,  however,  seemed  to  be  the  most  satisfactory.  Steel  caps, 
EEE  serve  to  tighten  the  plungers.  MM  are  receptacles  for  thermometers 
for  measuring  the  temperature.  C  is  an  iron  air-bath  and  protects  the  cell 
from  rapid  changes  in  temperature. 

In  heating  a  cell  of  this  kind  it  was  found  that  the  rise  in  temperature  should 
be  very  gradual.  Very  great  difficulty  was  encountered  in  getting  the  ends  to 
hold  liquid  tight.  The  screw  ends  were  tightened  gradually  for  several  days 
and  for  several  heatings.  On  one  occasion,  when  the  tube  was  filled  with  one 
of  the  higher  alcohols,  a  very  effective  closing  was  made.  It  is  possible  that 
dried  films  of  oils  (like  linseed  oil)  might  be  of  use  as  washers. 


FIG.  4. 

In  beginning  the  work  no  serious  trouble  from  the  formation  of  precipi- 
tates was  anticipated.  This  interference  was  encountered  and  a  new  form  of 
cell  is  being  made  which  it  is  hoped  will  overcome  some  of  the  imperfections  of 
the  form  above  described.  In  this  form  (fig.  4)  the  quartz  ends  are  fastened  in 
the  ends  Ef  in  the  same  way  as  in  fig.  3.  Instead  of  the  plunger  P  having  guide 
pins  it  has  guide  grooves.  Part  of  the  plunger  has  screw  threads,  by  means  of 
which  it  can  be  taken  out.  The  whole  cap  can  be  removed  from  the  tube  T  by 
unscrewing  E',  during  which  the  quartz  end  is  untouched.  When  the  ends  are 
removed  the  quartz  window  can  easily  be  cleaned.  Gold  washers  are  required 
here  between  T  and  E'  and  between  E'  and  C7. 

The  remaining  parts  of  fig.  4  represent  a  diagrammatic  arrangement  of 
the  apparatus.  Only  the  cell  is  drawn  to  scale.  The  cell  was  kept  in  a  hori- 
zontal position  so  that  all  bubbles  that  form  would  rise  in  the  side  tube.  As 


30  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

the  spectroscope  (containing  the  grating  G,  photographic  plate  holder  C,  and 
slit  S)  was  kept  in  a  vertical  position,  a  45°  quartz  prism  was  used  to  change 
the  horizontal  beam  of  light  into  a  vertical  beam,  the  beam  being  totally 
reflected  by  the  hypothenuse  surface  of  Q.  The  source  of  light  N.G.  (Nernst 
glower)  or  S.G.  (spark  gap)  was  focused  by  the  concave  speculum  mirror  M 
on  the  slit  S.  A  similar  arrangement  was  used  with  the  fused  silica  cell. 
D.T.S.  represents  a  double  throw  switch,  by  means  of  which  either  the  Nernst 
glower  or  the  spark  gap  may  be  thrown  in  circuit.  B  is  a  ballast.  R  is  a 
variable  resistance,  by  means  of  which  the  current  (read  by  the  ammeter  A) 
in  the  Nernst  glower  may  be  kept  constant. 

O.C.  is  an  oil  condenser.  Some  trouble  was  given  by  the  condensers, 
especially  when  a  large  spark  gap  (2  or  more  centimeters)  was  used  for 
several  hours.  Paraffin  condensers  often  become  heated  so  that  the  paraffin 
melts.  A  condenser  was  made  of  transformer  oil.  Unfortunately,  the  box 
part  was  made  of  wood  and  it  is  very  difficult  to  prevent  the  leaking  of  the 
oil  from  such  a  box,  especially  when  it  becomes  heated.  I.C.  is  an  X-ray 
induction  coil  and  Rt  is  a  resistance  in  the  primary  circuit  of  this  coil. 

Some  preliminary  tests  were  made  with  the  cells  at  high  pressure.  The 
Cailletet  pump  belonging  to  the  University  was  used  for  this  purpose,  the  cell 
represented  in  fig.  3  being  made  so  as  to  fit  on  this  pump.  It  was  not  at  all 
difficult  to  obtain  pressures  of  200  atmospheres  with  water  and  alcohol  solu- 
tions. Spectrograms  were  made  of  the  absorption  spectra  of  neodymium  solu- 
tions under  pressures  as  high  as  275  atmospheres.  No  effect  of  pressure  was 
detected.  The  work  at  high  pressures  is  easier  than  at  high  temperatures,  on 
account  of  the  fact  that  there  is  no  expansion  of  the  cell  due  to  heating. 


CHAPTER   III. 

MAPPING  THE  ABSORPTION  SPECTRA  OF  VARIOUS 
SALTS  IN  SOLUTION. 

An  accurate  knowledge  of  the  absorbing  power  of  solutions  is  the  first 
requisite  in  understanding  the  nature  of  absorption,  and,  accordingly,  the 
mapping  of  the  spectrum  is  the  first  thing  to  be  done.  This  has  been  accom- 
plished for  a  large  number  of  solutions,  but  there  are  quite  a  few  salts  that 
have  thus  far  been  omitted,  and  it  is  the  purpose  of  this  chapter  to  give  the 
results  with  some  of  these  solutions.  This  has  been  made  possible  largely 
through  the  kindness  of  Professor  Urbain,  who  has  loaned  us  the  oxides  of 
samarium,  dysprosium,  and  gadolinium.  Dr.  Guy  has  converted  these  oxides 
into  the  various  salts  such  as  the  chloride,  nitrate,  etc.,  and  has  dissolved  these 
in  various  solvents.  The  other  salts  whose  absorption  spectra  have  been  inves- 
tigated have  been  obtained,  for  the  most  part,  from  Kahlbaum.  The  numbers 
of  plates  described  in  this  chapter  run  from  1  to  34  inclusive. 

Jones  and  Anderson  have  shown  that  the  absorption  bands  of  a  given 
salt  in  any  solvent  were  characteristic  of  that  solvent.  For  this  reason  the 
photographing  of  the  absorption  spectra  of  a  given  salt  in  different  solvents 
will  be  considered  as  the  mapping  of  characteristic  spectra.  On  the  other 
hand,  when  a  salt  is  gradually  changed  to  another  salt  by  the  addition  of  an 
acid  to  the  solution,  or  by  the  addition  of  a  foreign  salt,  the  absorption  bands 
show  gradual  changes.  This  has  been  interpreted  as  being  due  to  changes  in 
the  molecular  aggregates  of  the  salts,  and  to  the  formation  of  intermediate 
compounds.  These  changes  are  considered  as  being  of  a  chemical  nature, 
and  will,  therefore,  be  taken  up  in  the  chapter  dealing  with  the  spectrophotog- 
raphy  of  chemical  reactions;  and  the  facts  there  described  will  be  regarded  as 
furnishing  strong  evidence  for  the  existence  of  molecular  clustering  in  liquids, 
and  also  for  the  theory  that  the  absorption  and  emission  centers  of  spectrum 
bands  consist  of  more  or  less  complex  atomic  or  molecular  aggregates,  probably 
in  a  process  of  ionization.  The  full  development  of  this  view  appears  in  the 
summary. 

The  experimental  methods  are  essentially  those  described  in  Publication 
130  of  the  Carnegie  Institution  of  Washington,  and  in  the  chapter  on  experi- 
mental methods  in  this  monograph.  Nothing  more  need  be  said  here,  except 
that  it  would  probably  be  desirable  in  some  cases  to  place  the  negative  film 
of  an  absorption  spectrum  just  below  the  photographic  film  that  is  being 
exposed.  Then,  by  lengthening  the  time  of  exposure  very  greatly,  it  should 
be  possible  to  get  a  spectrogram  containing  a  great  many  bands. 

THE  ABSORPTION  OF  CERTAIN  CYANIDES  AND  CHROMATES. 

The  early  workers  on  absorption  spectra  supposed  that  if  two  salts,  dis- 
solved in  the  same  solvent,  had  absorption  bands  that  were  close  together, 
the  wave-lengths  of  the  bands  would  be  modified  by  the  salts  being 
together  in  the  solution.  Experiments  of  this  kind  have  been  made  without 

31 


32  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

much  success.  According  to  the  theory  of  aggregates,  however,  it  would  not 
be  expected  that  any  very  marked  effect  would  result,  unless  the  two  salts 
formed  parts  of  the  same  aggregate;  the  term  aggregate  being  used  in  the 
broader  sense  here  to  include  also  molecules  of  the  solvent.  Accordingly,  the 
list  of  colored  chemical  compounds  was  searched  for  salts  that  contained 
colored  anions  and  colored  cations.  An  effort  was  also  made  to  obtain  solvents 
and  salts  that  had  bands  in  the  same  part  of  the  spectrum.  So  far  no  good 
examples  were  found  where  the  same  spectral  aggregates  contained  different 
absorbing  centers  that  possess  bands  in  the  same  region  of  the  spectrum.  It 
seems  quite  possible,  however,  that  aggregates  of  this  kind  among  organic 
compounds  could  be  found,  or  that  in  the  infra-red  region  many  examples  of 
this  kind  will  be  found.  The  region  of  the  infra-red  is  especially  inviting  for 
work  of  this  kind,  inasmuch  as  nearly  all  groups  possess  bands,  and  the 
absorbers  seem  to  be  of  molecular  dimensions ;  whereas  in  the  visible  portion 
of  the  spectrum  it  seems  probable  that,  in  most  cases  at  least,  the  constitution 
of  the  spectral  aggregate  only  influences  the  period  of  vibrators  that  seem  to 
be  of  the  nature  of  electrons. 

It  has  been  shown  that  the  presence  of  calcium  or  aluminium  chloride  has 
a  considerable  influence  upon  the  wave-lengths  of  the  uranyl  chloride  bands. 
This  has  been  explained1  as  being  due  to  the  presence  of  chlorine,  rather  than 
to  the  direct  presence  of  the  calcium  or  aluminium  atoms.  It  is  possible  to 
obtain  aqueous  solutions  of  calcium  ferricyanide  or  of  aluminium  and  calcium 
chromate.  If  the  change  of  wave-lengths  of  the  uranyl  bands  was  not  due  to 
calcium  and  aluminium,  then  the  absorption  of  the  potassium,  aluminium,  and 
calcium  ferricyanides  and  chromates  should  be  the  same.  These  salts  were 
studied  to  test  whether  or  not  this  was  the  case. 

The  dissociation2  of  the  ferricyanides,  ferrocyanides,  and  chromates  is 
an  interesting  one,  and  the  study  of  the  absorption  spectra  of  solutions  of 
these  salts,  especially  in  the  infra-red,  will  probably  throw  much  light  upon 
this  subject,  but  in  this  work  time  did  not  permit  us  to  take  up  this  problem. 

CALCIUM  FERROCYANIDE  AND  CALCIUM  FERRICYANIDE. 

The  absorption  spectrum  of  calcium  ferricyanide  is  given  in  plate  2,  A, 
and  of  calcium  ferrocyanide  in  plate  2,  B.  The  concentrations  are  given  in 
the  chapter  on  the  description  of  plates.  Starting  with  strip  1  of  A,  the  edge 
of  the  absorption  band  is  at  about  X  4700;  the  concentration  (c)  being  0.031 
normal  and  the  depth  of  cell  (d)  24  mm.  (hereafter  the  product  cd  will  be 
given  without  definition,  c  being  expressed  in  terms  of  normal  and  d  in  milli- 
meters), the  value  of  cd  being  0.74.  In  the  case  of  potassium  ferricyanide3 
for  a  value  of  cd  of  0.69  the  edge  of  the  absorption  band  comes  at  about 
X4690,  considering  the  limit  of  absorption  as  at  X4710  and  the  distance  be- 
tween this  limit  and  the  place  where  the  absorption  is  50  per  cent  as  being  20 
Angstrom  units.  It  is  thus  seen  that  the  absorption  of  calcium  ferricyanide 
is  approximately  the  same  as  that  of  potassium  ferricyanide.  The  conclusion 
follows  that  calcium  shows  no  bathochromous  effect  in  this  instance. 


'Phys.  Zeit.,  M,  668  (1910). 

2  Publication  130,  Carnegie  Institution  of  Washington,  28  and  29. 

"  Ibid.,  29. 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  33 

In  strip  1,  B,  plate  2,  cd  is  6  and  the  middle  of  the  edge  of  absorption  is  at 
about  X  4150,  the  edge  of  the  band  being  about  300  Angstrom  units  wide.  The 
edge  of  the  absorption  is  very  wide  and  diffuse,  resembling  the  absorption  of 
potassium  ferrocyanide.  No  direct  comparison  of  the  absorption  in  the  two 
cases  can  be  made,  as  the  value  of  cd  is  much  larger  in  the  case  of  the  calcium  salt. 

THE  CHROMATE  AND  BICHROMATE  OF  LITHIUM. 

The  absorption  spectrum  of  an  aqueous  solution  of  lithium  chromate  is 
given  in  A,  plate  1,  and  of  lithium  bichromate  in  B,  plate  1.  In  the  case  of 
lithium  chromate  a  change  in  cd  of  0.75  to  6.0  produces  an  increase  in  width  of 
the  absorption  of  over  200  Angstrom  units;  the  edge  of  the  band  being  at  about 
X  4850  for  cd  =  0.75.  This  is  approximately  the  position  of  the  edge  of  the 
absorption  band  of  potassium  chromate  for  a  corresponding  value  of  cd.  For 
lithium  bichromate,  the  edge  of  the  absorption  for  strip  1,  cd  =  0.75  is  about 
X  5350.  The  values  of  cd  here  are  much  larger,  and  the  absorption  is,  therefore, 
much  greater  than  in  the  case  of  potassium  bichromate  previously  investigated. 

ALUMINIUM  AND  CALCIUM  CHROMATES. 

The  absorption  spectrum  of  an  aqueous  solution  of  aluminium  chromate 
is  given  in  A,  plate  3.  The  depths  of  cell  are  3,  24,  24,  and  24  mm.  Starting 
with  the  lowest  strip  the  solution  used  in  strip  1  was  the  same  as  in  strip  2. 

In  B,  plate  3,  is  given  the  absorption  of  an  aqueous  solution  of  calcium 
chromate,  the  depths  of  cell  being  24  mm.  and  the  concentrations  0.025,  0.033, 
0.046,  0.066,  0.1,  0.15,  and  0.2  normal.  For  a  value  of  cd  of  0.6  the  edge  of  the 
absorption  is  at  about  X  4670.  For  corresponding  values  of  cd  it  seems,  there- 
fore, that  the  absorption  of  calcium  chromate  is  less  than  the  absorption  of 
lithium  or  potassium  chromate,  and  that  the  presence  of  calcium  does  not 
increase  the  width  of  the  absorption  bands. 

POTASSIUM  NICKEL  CHROMATE  AND  COPPER  BICHROMATE. 
The  absorption  of  these  two  salts  is  an  example  of  the  absorption  of  salts 
in  which  both  the  anion  and  the  cation  are  colored.  A,  plate  4,  represents  the 
absorption  of  an  aqueous  solution  of  copper  bichromate,  the  depths  of  cell 
being  3,  24,  24,  24,  24,  24,  and  24  mm.  and  the  concentrations  0.044,  0.044, 
0.08,  0.117,  0.175,  0.26,  and  0.35  normal.  B  gives  the  absorption  of  an  aqueous 
solution  of  potassium  nickel  chromate.  A  is  seen  to  show  the  edge  of  the  red 
copper  band.  For  a  value  of  cd  of  0.13,  the  edge  of  the  absorption  in  the  blue 
is  about  X  4900,  which  is  seen  to  be  about  the  same  as  that  for  potassium 
bichromate.  The  absorption  of  salts  having  both  ions  colored  does  not  seem 
to  be  at  all  different  from  what  one  would  expect  if  the  absorption  was  addi- 
tive. Of  course,  these  experiments  are  very  largely  qualitative,  and  it  is 
expected  that  a  rigorous  examination  along  quantitative  lines  will  be  made 
with  the  radiomicrometer.  For  photographic  methods  the  above  salts  are 
not  at  all  well  suited,  since  the  limits  of  absorption  and  transmission  are  very 
large  and  ill  defined. 

THE  ABSORPTION  OF  SOLUTIONS  OF  CERTAIN  ERBIUM  SALTS. 
On  account  of  the  slight  solubility  of  the  erbium  chloride  in  the  higher 
alcohols  and  other  organic  solvents,  very  few  solutions  could  be  made  of 
sufficient  concentration  to  show  the  erbium  absorption  bands.     Several  of 
3 


34  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

these  will  be  taken  up  under  the  effect  of  change  in  temperature  on  absorption 
spectra. 

Hofmann  and  Kirmreuther1  have  examined  the  absorption  spectra  of 
certain  salts  of  erbium,  using  the  reflection  method,  and  find  a  very  marked 
similarity  between  the  spectra  of  all  of  the  salts  investigated,  although  these 
may  be  as  different  as  the  chloride  and  sulphide  of  erbium.  For  this  reason 
they  conclude  that  the  erbium  bands  are  due  to  locked  electrons  and  not  to 
saturated  valency  electrons. 

THE   ABSORPTION    OF    SOLUTIONS  OF   CERTAIN    NEODYMIUM    SALTS. 

Previous  work  has  shown  us  that  neodymium  and  uranous  salts  show 
characteristic  solvent  spectra  better  than  any  other  colored  salts.  On  account 
of  the  sharpness  of  the  neodymium  bands,  neodymium  salts  have  been  made 
the  object  of  especial  study  for  the  existence  of  solvent  spectra.  In  many 
cases  it  is  known  how  the  neodymium  bands  break  up  in  a  magnetic  field, 
and  in  general  it  is  probably  true  that  the  absorption  of  salts  of  this  element 
has  been  studied  more  than  that  of  any  of  the  others.  It  seems,  therefore, 
probable  that  ultimately  some  knowledge  of  the  forces  within  the  solvate  may 
be  learned,  when  it  is  found  how  the  various  neodymium  bands  are  broken 
up  for  the  different  kinds  of  solvates.  In  the  following  pages  considerable 
emphasis  will  be  laid  upon  the  finer  structure  of  the  neodymium  bands  for 
solutions  in  the  various  solvents.  A  large  field  of  investigation  is  open  for  the 
study  of  the  difference  in  the  structure  of  these  bands  in  solids  and  especially 
in  crystals.  Only  a  few  examples  of  the  latter  kind  will  be  described  here. 

In  the  description  of  the  groups  of  neodymium  absorption  bands,  the 
following  nomenclature  will  be  used.  This  is  done  for  the  reason  that  each 
one  of  these  groups  of  bands  possesses  a  characteristic  structure  for  the  various 
solvents,  and  very  often  for  different  salts  in  the  same  solvent.  While  the 
groups  of  bands  do  not  change  greatly  in  relative  intensities,  the  finer  bands 
in  each  group  show  most  extraordinary  changes  of  this  kind.  The  a  group 
includes  bands  in  the  region  X  3400  to  X  3600;  the  /3  group  the  bands  at 
about  X  4300;  the  7  group  from  X  4600  to  X  4800;  the  5  group  from  X  5000  to 
X  5400;  the  e  group  in  the  region  X5800  and  the  C  group  at  X6300.  In  the 
general  discussion  of  results  these  groups  will  be  compared  under  various 
conditions  of  temperature,  solvent,  acid,  etc. 

In  the  measurements  of  the  wave-lengths  of  the  neodymium  bands,  the 
standard  spark  lines  were  photographed  only  in  the  ultra-violet,  so  that  the 
measurements  of  the  long  wave-length  bands  here  given  are  not  claimed  to 
be  very  accurate  and  are  made  largely  for  comparison.  On  the  other  hand, 
the  difference  in  wave-length  of  bands  in  the  same  group  is  much  more  accurate. 

In  designating  the  groups  of  bands  of  the  neodymium  spectra,  previous 
workers  started  with  the  red  end  of  the  spectrum.  This,  however,  is  an  un- 
natural method  of  procedure  when  a  grating  is  used,  since  the  spectrograms 
are  all  printed  with  the  short  wave-lengths  on  the  left  side,  with  the  wave- 
lengths increasing  linearly  as  we  pass  towards  the  right.  Moreover,  it  is  very 
doubtful  if  the  ultra-violet  absorption  spectra  of  neodymium  can  be  investi- 
gated much  farther  in  this  region,  so  that  this  is  the  natural  end  of  the  spectrum 

1  Zeit.  phys.  Chem.,  71,  312  (1910). 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  35 

from  which  to  begin  naming  the  groups  of  bands.  On  the  other  hand,  it  is 
very  probable  that  there  are  many  more  neodymium  bands  in  the  infra-red, 
and  if  these  occur  in  groups,  these  groups  can  then  be  named  in  their  proper 
order.  The  reason  that  the  uranyl  series  of  absorption  bands  was  named  in  the 
opposite  direction  was  on  account  of  the  fact  that  the  strongest  of  these  bands 
are  at  the  red  end  of  the  series,  while  the  weak  bands  are  in  the  ultra-violet, 
the  weaker  ones  of  the  series  in  many  cases  still  remaining  to  be  photographed. 

NEODYMIUM  CHLORIDE  IN  WATER. 

Some  of  the  weak  and  fine  bands  of  neodymium  and  uranium  are  extremely 
difficult  to  obtain  clearly  on  a  photographic  plate,  and  it  has  sometimes  seemed 
to  us  that  the  presence  of  absorption  bands  of  some  wave-lengths  might  be 
due  to  some  absorber  that  was  not  always  present  in  the  solution.  For  in- 
stance, the  presence  or  absence  of  foreign  nuclei  might  be  a  determining  factor 
in  the  constitution  of  the  aggregates.  It  might  also  be  possible  that  aggregates 
in  solution  are  quite  stable  as  far  as  their  inner  constitution  is  concerned,  so 
that  an  aqueous  solution  of  neodymium  chloride,  for  instance,  might  show 
different  absorption  bands  depending  upon  what  the  species  of  neodymium 
chloride  aggregates  was  before  the  salt  was  dissolved.  It  might  be  possible 
to  detect  phenomena  of  this  kind. .  It  would  also  be  very  interesting  to  find 
whether  there  is  any  relation  between  the  kinds  of  spectral  aggregates  of  a 
salt  in  solution,  and  the  ionic  and  nucleating  centers  produced  by  spraying 
or  bubbling  the  solution.  Nuclei  of  various  salts  have  been  investigated  in 
this  manner  by  Broglie  and  others.  The  spray  from  solutions  of  the  same  salt 
in  two  or  more  solvents  could  be  taken  up.  Samarium  and  uranous  salts  could 
be  studied  in  the  same  manner. 

Plate  60,  B,  in  the  original  film  shows  bands  at  XX  4000,  4180,  4271,  4280, 
4295,  4330,  4650,  4695,  4805,  5330,  etc.  So  far  as  we  remember,  this  is  the 
first  plate  of  an  aqueous  solution  on  which  the  very  narrow  and  faint  band 
at  X  4280  has  clearly  appeared.  The  band  X4805  is  also  a  very  weak  one.  In 
the  first  strip  of  the  original  film,  the  band  X  4271  possessed  very  sharp  edges 
and  was  about  8  Angstrom  units  in  width.  The  band  X  4280  was  very  weak 
and  was  not  more  than  1.5  or  2  Angstrom  units  wide.  The  band  X4295,  on 
the  other  hand,  was  about  8  Angstrom  units  wide  and  very  weak.  X  4650  is 
very  weak  and  is  seldom  seen. 

An  attempt  will  be  made  to  compare  as  much  in  detail  as  possible  the 
bands  at  X4280,  X5200,  and  X5800  for  the  various  solvents,  since  it  is  these 
bands  that  give  evidences  of  the  existence  of  solvates  and  the  various  aggregates. 

NEODYMIUM  CHLORIDE  AS  A  METHYL  ALCOHOLATE. 

A  solution  of  neodymium  chloride  in  methyl  alcohol,  that  had  been 
allowed  to  stand  over  the  summer,  was  found  to  contain  a  gelatinous  precipi- 
tate. The  absorption  spectrum  was  found  to  show  the  neodymium  bands  quite 
sharply,  these  bands  having  a  somewhat  different  appearance  from  those  in 
an  ordinary  methyl  alcohol  solution. 

A  sharp  band  appears  at  X4270,  a  weaker  band  about  8  Angstrom  units 
wide  at  X4295;  a  wide  weak  band  at  X3440;  the  triplets  at  XX  4700,  4760,  and 
4830;  a  very  weak  band  at  X5100;  a  wide  hazy  band  at  X5140;  two  strong, 
sharp  bands  at  X5220  and  X  5235;  a  wide  and  weak  band  at  X5260,  and  bands 
more  or  less  blurred  together  at  XX  5704,  5780,  5815,  and  5860.  It  will  be  noticed 


36  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

that  the  bands  at  X4270  and  X4295  are  relatively  stronger  than  usual.  The 
appearance  of  these  two  bands  suggests  that  the  precipitate  is  largely  the 
hydrate  of  neodymium  chloride,  the  band  X4270  being  a  water  band,  and 
the  band  X4295  being  an  alcohol  band. 

NEODYMIUM  CHLORIDE  IN  PROPYL  ALCOHOL. 

The  only  spectrogram  of  the  absorption  spectra  of  neodymium  chloride 
in  propyl  alcohol  that  is  reproduced  is  that  of  A,  plate  7. 

The  a  group  is  composed  of  the  following  bands :  X  3445,  a  rather  sharp 
band  about  4  Angstrom  units  in  width;  X  3460,  about  10  Angstrom  units  in 
width;  X  3490  of  about  the  same  intensity  and  width  as  X  3460;  X  3510  very 
weak;  X  3525  about  4  Angstrom  units  wide  and  quite  strong;  X  3540  quite 
strong  and  narrow,  this  band  almost  running  into  the  more  diffuse  band  at 
X  3560;  a  very  weak  band  appears  at  about  X  3580.  The  /3  group  is  quite 
characteristic  of  the  solvent,  consisting  of  a  very  weak  band  at  about  X  4270, 
a  band  at  X  4285  about  10  Angstrom  units  wide,  and  a  much  wider  and  weak 
band  at  about  X  4330;  a  wide  and  weak  band  appears  at  X  4450.  The  7  group 
consists  of  a  very  weak  and  diffuse  band  at  X  4600,  and  other  bands  at  X  4700, 
X4770,  and  X4830.  The  5  group  consists  of  two  wide  and  diffuse  bands  at 
X  5130  and  X  5180,  the  latter  being  very  weak;  and  finer  bands  at  X  5220, 
X  5230,  X  5250,  X  5290  and  a  very  weak  band  at  X  5330.  The  e  group  consists 
of  the  four  bands  X  5740,  X  5780,  X  5810,  and  X  5850,  all  being  of  about  the 
same  width,  the  latter  two  being  considerably  the  stronger.  There  are  other 
bands  in  the  red  region,  but  only  X  6880  is  at  all  strong. 

NEODYMIUM  CHLORIDE  IN  ISOPROPYL  ALCOHOL. 

A,  plate  6,  gives  the  absorption  spectrum  of  neodymium  chloride  in  iso- 
propyl  alcohol.  The  finer  structure  of  the  different  groups  of  bands  is  quite 
different  from  that  of  the  propyl  alcohol  spectrum. 

The  a  group  of  this  alcohol  is  very  simple,  showing  only  three  hazy  bands, 
at  X  3460,  X  3510,  and  X  3535,  the  middle  band  being  much  the  weaker.  Only 
a  single  band  of  the  0  group  shows,  X  4265.  Other  bands  appear  at  X  4420, 
X4600  very  diffuse,  X4690  and  X4730. 

The  8  group  consists  of  X5100  and  X5320.  These  bands  are  quite  wide 
and  diffuse.  On  account  of  the  plate  not  being  properly  developed  the  bands 
do  not  show  as  much  detail  as  they  probably  would  under  more  favorable 
conditions.  Even  this  plate  shows  the  finer  bands  slightly. 

The  t  group  consists  of  a  broad  diffuse  band  at  X  5720  and  two  much 
stronger  bands  at  X  5780  and  X  5810. 

NEODYMIUM  CHLORIDE  IN  BUTYL  ALCOHOL. 

The  absorption  spectrum  of  neodymium  chloride  in  butyl  alcohol  is  given 
in  plate  5,  A.  Starting  with  the  ultra-violet,  we  have  X3450  very  sharp  and 
narrow;  X  3460  weak;  X  3492  somewhat  diffuse;  X  3535  very  sharp  and  narrow; 
X  3545,  X  3560  very  diffuse.  The  bands  XX  4265,  4285,  and  4300  are  weak  and 
of  approximately  the  same  intensity,  the  band  X  4265  being  slightly  narrower 
than  the  other  two.  These  bands  differ  not  only  in  relative  intensity  from 
the  water  bands  but  also  in  wave-length,  band  X  4265  being  of  shorter  wave- 
length and  the  band  X  4300  of  greater  wave-length  than  the  water  bands. 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  37 

The  other  bands  are  quite  diffuse  and  appear  at  XX  5085  (narrow),  5095 
(narrow  and  very  weak),  5130,  5200,  5215,  5240,  5270,  5300,  5710,  5750, 
5780,  5820,  5860,  5900,  and  5930. 

This  plate  is  described  in  detail  in  the  chapter  at  the  end  of  the  mono- 
graph. It  may  be  noticed  that  for  the  solution  of  greatest  length,  the  absorp- 
tion in  the  ultra-violet  is  very  strong,  extending  to  X  4100.  This  is  probably 
due  to  the  propyl  alcohol.  It  is  certainly  not  due  to  the  absorption  of  the 
neodymium  chloride  itself. 

NEODYMIUM  CHLORIDE  IN  ISOBUTYL  ALCOHOL. 

A,  plate  8,  represents  the  absorption  spectrum  of  neodymium  chloride 
in  isobutyl  alcohol.  It  will  be  seen  from  the  wave-lengths  given  below  that 
there  are  quite  marked  differences  between  the  absorption  in  this  alcohol  and 
that  in  butyl  alcohol.  The  band  X  3455  is  about  10  Angstrom  units  wide,  and 
is  quite  weak  in  the  above  photograph,  X  3485  is  of  about  the  same  width  and 
is  much  stronger,  X3515ois  very  weak,  XX  3545  and  3570  are  of  about  the  same 
intensity  and  each  10  Angstrom  units  wide.  There  seems  to  be  a  very  weak 
band  at  about  X  4300.  Wide  and  very  diffuse  bands  appear  at  XX  4550,  5120, 
5220,  5250,  5720,  5780,  5800,  5850,  and  5890.  The  four  bands  last  mentioned 
are  of  about  equal  intensity. 

The  general  characteristics  of  the  absorption  spectrum  of  neodymium 
chloride  in  isobutyl  alcohol  are  the  weakness  and  diffuseness  of  the  bands  in 
general,  their  different  relative  intensities  compared  with  butyl  alcohol  bands, 
and  their  slightly  greater  wave-lengths.  The  butyl  alcohol  bands  are  very 
much  finer  and  sharper  than  the  isobutyl  alcohol  bands.  In  general,  it  seems 
that  the  shorter  the  wave-lengths  of  the  solvent  bands  the  finer  and  sharper 
are  those  bands. 

Another  spectrogram  taken  of  a  solution  containing  a  much  longer  layer 
contains  the  following  bands:  Theo0  group  X  4270,  a  very  weak  and  narrow 
band;  X4290,  a  weak  band  about  6  Angstrom  units  wide;  X4310,  the  strongest 
band  in  the  group,  being  a  little  stronger  than  X  4290;  X  4330  weak  and  quite 
diffuse,  completing  the  bands  of  this  group;  a  very  wide  (50  Angstrom  units) 
diffuse  band  appears  at  X  4450;  the  y  group  consists  of  bands  about  20  Ang- 
strom units  wide  at  X4700,  X4730,  X4780,  X4830,  and  X4880,  this  band  being 
very  weak;  the  5  bands  at  X 51 50  and  X5260  are  about  80  Angstrom  units  in 
width  and  consist  of  smaller  bands  that  appear  practically  fused  together; 
some  of  the  finer  bands  being  at  X  5215,  X  5230,  X  5250,  and  X5300;  the  c  group 
composed  of  the  following  bands:  X  5740  rather  weak,  X5810  strong,  X  5850 
strong,  X  5890,  X  5920,  X  5950  very  weak,  X  5995  very  weak,  and  X  6020  very 
weak. 

The  ultra-violet  absorption  of  isobutyl  alcohol  is  very  considerable  and 
prevents  the  a  bands  from  being  shown  very  plainly.  The  smaller  bands  are 
also  more  numerous,  although  weaker  than  in  most  other  solvent  spectra. 

NEODYMIUM  CHLORIDE  ix  ETHER. 

Neodymium  chloride  is  only  very  slightly  soluble,  if  soluble  at  all,  in  ordi- 
nary ether.  By  adding  a  small  amount  of  a  concentrated  solution  of  neodym- 
ium chloride  in  methyl  alcohol  to  ether,  a  solution  of  about  0.01  normal  was 
obtained.  At  about  10°  C.  this  solution  is  transparent  and  its  absorption  was 


209174 


38  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

photographed.  Heated  to  about  35°  C.  a  white  precipitate  was  formed,  mak- 
ing the  solution  quite  opaque.  When  cooled  again  the  solution  became  trans- 
parent. A  solution  of  this  kind  might  serve  to  give  us  a  better  knowledge  of 
the  constitution  of  aggregates.  Suppose  it  could  be  shown,  spectroscopically, 
that  the  neodymium  chloride  aggregates  existed  in  the  ether  as  the  methyl 
alcoholate,  and  that  when  the  cloud  was  formed  the  ether  solution  was  com- 
pletely freed  from  any  neodymium  salt.  The  number  of  cloud  particles 
could  easily  be  counted  with  an  ultra-violet  microscope  and  the  size  of  the 
neodymium  aggregates  thus  approximately  determined.  A  study  of  the 
Brownian  movements  and  the  growth  of  such  a  cloud  would  also  be  interect- 
ing.  It  might  be  possible  in  some  case  to  obtain  a  transparent  solution  of 
colored  solvates  in  a  solvent  having  the  same  index  of  refraction  and  density 
as  the  solvate,  but  not  miscible  with  it,  and  by  heating  such  a  solution  the 
liquid  of  the  solution  and  the  solvate  might  mix  at  higher  temperatures  and 
the  resultant  salt  aggregate,  if  insoluble,  would  then  be  precipitated. 

NEODYMIUM  NITRATE  IN  PROPYL  ALCOHOL. 

B,  plate  7,  represents  the  absorption  spectrum  of  neodymium  nitrate  in 
propyl  alcohol.  The  absorption  bands  of  this  spectrum  are  quite  diffuse  and 
present  a  sort  of  washed-out  appearance. 

The  a  group  consists  of  three  bands,  the  inner  band  being  the  wider  and 
weaker.  These  bands  are  nearly  20  Angstrom  units  wide  and  are  located  at 
X3455,  X3500,  and  X3585.  The  0  group  consists  of  but  a  single  band  about  12 
Angstrom  units  in  width  at  about  X  4268.  The  7  and  other  bands  in  that 
region  are  very  broad  and  weak.  The  5  group  is  resolvable  into  the  single  bands 
X  5100  and  X  5220.  For  the  greater  concentrations,  however,  two  bands  can  be 
distinguished  near  the  center  of  X  5220,  being  at  about  X  5220  and  X  5235. 
The  e  group  consists  of  the  hazy  bands  X  5700,  X  5750,  X  5780,  and  X  5810. 

NEODYMIUM  NITRATE  IN  ISOPROPYL  ALCOHOL. 

The  absorption  spectrum  of  neodymium  nitrate  in  isopropyl  alcohol 
resembles  quite  closely  the  general  diffuseness  of  the  propyl  alcohol  spectrum 
previously  described. 

The  a  group  consists  of  three  ohazy  bands  at  X3460,  X3505,  and  X3535. 
Each  of  these  bands  is  about  15  Angstrom  units  in  width.  The  0  band  is 
weak,  being  located  at  X  4270.  Bands  appear  at  X  4430,  X  4690  and  X  4730. 
The  5  group  consists  of  a  band  at  X  5100  and  one  at  X  5230.  The  latter  con- 
sists of  a  wide,  diffuse,  short  wave-length  component,  and  two  finer  bands 
that  resemble  very  closely  the  corresponding  propyl  alcohol  bands.  The  e 
group  consists  of  a  weak  hazy  band  at  X  5720,  and  two  stronger  bands  at  X  5790 
and  X  5810. 

NEODYMIUM  NITRATE  IN  BUTYL  ALCOHOL. 

The  absorption  spectrum  of  neodymium  nitrate  in  butyl  alcohol  is  given 
in  the  first  two  strips  of  A,  plate  9.  The  general  characteristics  of  the  bands 
is  their  general  diffuseness. 

The  a  group  consists  of  three  diffuse  bands,  the  outer  bands  being  much 
the  strongest  at  XX  3450,  3500,  and  3540.  The  0  group  consists  of  a  band  at 
about  X  4265,  and  a  very  weak  band  at  about  X  4280.  Weak  and  diffuse  bands 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  39 

appear  at  X  4420,  X  4690,  X  4730,  and  X  4820.    The  other  bands  are  at  X  5090, 
X  5220,  X  5710,  X  5800,  and  X  5930. 

The  absorption  spectrum  of  neodymium  nitrate  in  butyl  alcohol  resembles 
very  closely  the  spectrum  in  isopropyl  alcohol,  but  is  quite  different  from 
the  spectrum  in  isobutyl  alcohol. 

NEODYMIUM  NITRATE  IN  ISOBUTYL  ALCOHOL. 

The  absorption  spectrum  of  neodymium  nitrate  in  isobutyl  alcohol  is 
similar  to  that  of  the  chloride  in  the  same  alcohol.  The  bands  in  some  cases 
are  not  so  wide,  but  they  are  all  quite  weak  when  they  first  appear  in  the  spec- 
trum. The  ultra-violet  absorption  was  so  great  that  in  the  plate  taken  the 
a  group  does  not  appear  at  all.  At  X  4285  appears  a  weak  double  band  about 
15  Angstrom  units  wide.  These  bands  are  so  close  to  one  another  that  it 
is  difficult  to  be  certain  that  they  are  separate  bands.  There  are  also  very 
weak  bands  at  X  4305  and  X  4325.  The  /3  group  of  the  chloride  in  isobutyl 
alcohol  is  very  different  in  its  structure  from  that  of  the  /3  group  of  the 
nitrate.  A  very  weak  band  appears  at  X  4450  and  X  4600,  which  is  about  80 
Angstrom  units  wide.  The  y  group  consists  of  weak  bands,  each  about  20 
Angstrom  units  in  width  at  XX  4715,  4750,  4770,  and  4850.  The  8  group  con- 
sists of  the  wide  and  very  hazy  band  at  X  5120,  two  comparatively  weak  bands 
at  X5215  and  X5230,  and  three  strong  bands  that  practically  merge  into  each 
other  at  X  5245,  X  5255,  and  X  5275.  The  e  group  forms  a  single  wide  band 
extending  from  X  5730  to  X  5900.  Very  hazy  and  weak  bands  appear  at 
X  6000,  X  6050,  and  about  X  6800. 

The  composition  of  the  various  groups  of  the  nitrate  isobutyl  bands  is 
quite  different  from  the  chloride  bands.  This  is  a  general  phenomenon,  the 
nitrate  bands,  in  general,  being  quite  different  from  the  chloride  and  bromide 
bands  in  the  same  solvent. 

NEODYMIUM  NITRATE  IN  ACETONE. 

The  absorption  spectrum  of  neodymium  nitrate  in  acetone  also  consists 
of  wide,  diffuse,  and  weak  bands.  The  ultra-violet  absorption  is  large. 

The  following  bands  appear:  X4285  very  weak,  X  5130,  X  5250,  X  5750 
and  X  5840. 

NEODYMIUM  NITRATE  IN  ETHYL  ESTER. 

The  absorption  spectrum  of  neodymium  nitrate  in  ethyl  ester  is  given 
in  A  and  B,  plate  12,  and  B,  plate  10.  The  absorption  bands  of  this  spectrum 
are  in  general  quite  diffuse.  The  a  group  consists  of  three  hazy  bands,  the 
middle  one  being  much  the  weakest  at  XX  3455,  3500,  and  3540.  The  /3  group 
consists  of  a  single  band  about  15  or  20  Angstrom  units  wide  at  about  X  4270. 
The  bands  at  X  4440  and  X  4600  are  very  broad  and  weak.  The  7  group  is 
quite  different  from  the  y  group  of  other  solvents,  in  that  the  bands  are  not 
even  approximately  of  the  same  intensity  or  at  equal  distances  from  each 
other,  being  at  about  X  4710,  X  4730,  and  X  4830.  The  8  group  consisted  of 
X  5120,  X  5210,  X  5240,  and  X  5260.  The  e  group  consists  of  XX  5700,  5750, 
5780,  and  5810.  These  bands  are  very  diffuse,  about  20  Angstrom  units  wide, 
and  the  latter  two  are  much  the  stronger.  A  band  also  appears  at  X  5980. 

The  absorption  spectrum  of  neodymium  nitrate  in  methyl  ester  is  identical 
with  that  in  ethyl  ester. 


40  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

NEODYMIUM  ACETATE  IN  ACETONE. 

The  absorption  spectrum  of  neodymium  chloride  in  acetone  has  bands 
that  are  much  more  diffuse  than  the  corresponding  water  bands.  Similarly, 
the  acetone  bands  of  the  acetate  are  more  diffuse  than  the  water  bands,  and 
both  spectra  are  more  diffuse  than  the  chloride  spectra. 

The  a  group  of  the  acetate  in  acetone  apparently  consists  of  but  a  single 
band,  quite  weak,  at  X  4270  and  about  15  Angstrom  units  wide.  The  region 
X  4300  to  X  5100  is  practically  continuous,  the  bands  appearing  there  being 
so  weak  and  diffuse  that  they  can  hardly  be  detected.  The  5  group  consists 
of  a  wide  diffuse  band  at  X  5110  and  finer  bands  at  X  5200  (weak),  X  5235, 
X  5250,  and  X  5260;  the  latter  three  practically  blending  into  one.  The  e  group 
extended  from  X  5720  to  X  5860,  this  absorption  showing  a  weak  band  at 
X  5730,  about  30  Angstrom  units  in  width.  From  the  above  description  it 
will  be  noticed  that  there  is  a  strong  ultra-violet  absorption  (reaching  to 
X  3900),  and  that  the  neodymium  bands  themselves  are  very  wide  and  diffuse. 

NEODYMIUM  ACETATE  IN  FORMAMIDE. 

A,  plate  13,  represents  the  absorption  spectrum  of  neodymium  acetate  in 
a  formamide  solution.  The  absorption  bands  of  this  solution  are  quite  wide 
and  diffuse,  but  not  as  much  so  as  the  bands  of  the  acetate  in  acetone.  The 
ultra-violet  absorption  is  so  strong  as  to  prevent  the  appearance  of  the  a  group. 
The  /3  group  consists  of  a  band  at  X  4285,  which  is  about  10  Angstrom  units 
wide.  The  bands  XX  4440,  4690,  4750,  5110,  and  5230  are  wide,  diffuse,  and 
with  the  exception  of  the  latter,  are  all  very  weak.  The  e  group  consists  of 
four  diffuse  bands  that  run  into  each  other  at  XX  5710,  5740,  5790,  and  5830. 

SUMMARY  OF  NEODYMIUM  SPECTRA. 

a  Group  in  Water. — Neodymium  chloride  in  water  gives  X  3390  a  very 
weak  band,  X  3465  narrow  and  strong,  X  3505,  X  3540  narrow  and  strong,  and 
X  3560.  The  anhydrous  chloride  gives  a  rather  strong  and  narrow  band  at 
X  3500,  a  weaker  band  at  X  3537,  narrow  and  intense  bands  at  X  3570  and 
X  3595,  and  a  rather  hazy  band  at  X  3612. 

a  Group  in  Methyl  and  Ethyl  Alcohols. — The  chloride  shows  the  bands 
XX  3475,  3505,  and  3560.  These  bands  are  much  hazier  than  the  water  bands. 
The  latter  one  is  by  far  the  most  intense.  The  nitrate  in  methyl  alcohol  has 
two  bands,  X  3465  and  X  3545. 

a  Group  in  Acetone. — The  nitrate  has  rather  faint  and  wide  bands  at 
X  3475  and  X  3555. 

a  Group  in  Glycerol. — The  chloride  gives  a  weak  band  at  X  3520,  and 
strong  and  sharp  bands  at  X  3475  and  X  3550. 

/3  Group  in  Water. — Neodymium  chloride  in  water  gives  a  very  sharp 
band  at  X  4271,  and  a  very  narrow  and  weak  band  at  X  4290.  The  anhydrous 
salt  gives  narrow  and  intense  bands  at  X  4308  and  X  4313,  a  wider  band  at 
X  4333  and  a  narrow  band  at  X  4357.  Neodymium  nitrate  in  water  has  a  band 
at  about  X  4280,  which  is  more  hazy  than  the  X  4271  chloride  band,  and  which 
breaks  up  into  a  band  at  X  4271  and  a  sort  of  shading  on  the  red  side  of  this 
band  at  about  X  4280. 

j8  Group  in  Methyl  and  Ethyl  Alcohols. — A  band  appears  at  X  4290  about 
10  Angstrom  units  wide.  This  is  wider  and  fainter  than  the  water  band  at 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  41 

X  4271 .  X  4325  is  still  fainter  than  X  4290.  The  nitrate  in  methyl  alcohol  gives 
a  band  at  X  4280,  which  is  not  very  intense,  and  which  is  about  10  Angstrom 
units  wide. 

/3  Group  in  Acetone. — The  nitrate  has  the  band  X  4280  quite  weak  and 
about  15  Angstrom  units  wide. 

|8  Group  in  Glycerol. — This  group  in  glycerol  consists  of  a  sharp  and  very 
persistent  band  at  X  4288,  and  two  very  fine  bands  of  the  same  intensity  at 
X  4270  and  X  4305. 

7  Group  in  Water. — For  the  chloride  there  is  a  band  at  about  X  4610  with 
hazy  edges;  X  4645  a  very  weak  band;  a  band  at  X  4685  with  its  red  edge  the 
more  sharply  defined;  a  rather  sharp  band  at  X  4755  and  one  at  X  4820,  which 
is  narrow  and  quite  intense.  The  anhydrous  chloride  gives  faint  and  hazy 
bands  at  X  4640  and  X  4680,  narrow  and  intense  bands  at  X  4717,  X  4725,  X4735, 
X  4785,  X  4815,  and  X  4855.  The  nitrate  shows  bands  at  X  4737,  X  4755,  X  4772. 

7  Group  in  Methyl  and  Ethyl  Alcohols.— There  are  bands  at  X  4700,  X  4780, 
and  X  4825.  These  bands  are  of  about  the  same  intensity,  X  4780  being  some- 
what the  narrower.  X  4700  and  X  4825  have  faint  companions  to  the  violet. 
The  nitrate  shows  three  faint  bands  at  XX  4690,  4735,  and  4825. 

7  Group  in  Glycerol. — Glycerol  bands  of  the  chloride  appear  at  XX  4620, 
4710,  4730,  4760,  4790,  and  4840. 

5  Group  in  Water  (Green). — The  bands  in  this  group  form  a  rather  com- 
plicated series.    The  chloride  has  a  deep  narrow  band  at  X  5090,  a  wide  hazy 
band  at  X  5125,  a  pair  of  very  intense,  narrow  bands  at  X  5205  and  X  5222,  a 
narrow  band  at  X  5255,  and  a  faint,  hazy  band  at  X  5315.     The  anhydrous 
chloride  gives  a  weak  band  at  X  5088,  X  5117,  a  narrow,  intense  band  at  X  5147, 
X  5174,  X  5183,  X  5216,  X  5254,  X  5267,  X  5282,  etc.    The  nitrate  band  at  X  5090 
is  much  wider  and  hazier  than  the  corresponding  chloride  band,  whereas  the 
nitrate  band  at  X  5125  seems  narrower.    There  is  a  narrow  band  at  X  5205,  a 
much  more  intense  one  at  X  5225,  and  another  narrow  band  at  X  5235.    There 
seems  to  be  a  tendency  for  the  chloride  and  nitrate  spectra  to  become  much 
more  alike  as  the  dilution  is  increased. 

d  Group  in  Methyl  and  Ethyl  Alcohols. — These  bands  are  X  5125  hazy  and 
moderately  intense;  X  5180  hazy  and  fainter;  X  5220  intense  and  narrow; 
X  5245  intense  with  faint  companion  on  the  red;  X  5290  narrow  and  a  faint 
band  at  X  5315.  The  nitrate  has  two  rather  intense  bands  at  X  5225  and  X  5240. 

d  Group  in  Acetone. — The  nitrate  has  a  hazy,  but  rather  intense  band  at 
X  51 10,  X  5215,  and  X  5255. 

d  Group  in  Glycerol. — The  chloride  gives  bands  at  XX  5120  wide  and  hazy; 
5170  narrow;  5190  narrow;  5230,  5240,  5250,  and  5270  weak. 

€  Group  in  Water  (Yellow). — For  the  chloride,  this  group  consists  of  a 
narrow  and  quite  strong  band  at  X  5725,  a  strong  doublet  at  X  5745  and  X  5765, 
a  band  at  X  5795  very  similar  to  the  one  at  X  5725,  although  more  hazy.  The 
anhydrous  chloride  has  bands  at  X  5768,  X  5782,  a  narrow  and  intense  band  at 
X  5807,  X  5829,  a  narrow  band  at  X  5858,  etc. 

6  Group  in  Methyl  and  Ethyl  Alcohols.— This  group  consists  of  X  5725 
moderately  intense  with  hazy  edges;  X  5765  narrower;  X  5800  strong;  X  5835 
very  intense;  X  5860  hazy;  X  5895  faint;  X  5925  faint.    The  nitrate  shows  a 
band  at  X  5720,  probably  double,  a  band  from  X  5755  to  X  5845  and  at  X  5760, 
X  5835,  and  a  very  intense  band  at  X  5790. 


42  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

e  Group  in  Glycerol. — The  chloride  gives  the  following  bands:  XX  5740 
hazy,  5790,  5805,  5820,  and  5850. 

Although  the  absorption  spectra  of  the  dry  neodymium  salts  are  very 
different  from  one  another,  those  of  the  aqueous  solutions,  especially  when 
dilute,  are  very  much  the  same  for  the  different  salts.  For  concentrated 
solutions  the  chloride  is  very  similar  to  that  of  the  bromide,  but  these  are 
quite  different  from  the  nitrate. 

The  absorption  spectra  of  neodymium  chloride  in  methyl  alcohol  and  in 
ethyl  alcohol  are  practically  the  same,  and  differ  considerably  from  that  of 
the  nitrate.  The  absorption  bands  of  the  nitrate  in  ethyl  alcohol  are,  in 
general,  more  diffuse  than  in  methyl  alcohol. 

The  chloride  is  but  slightly  soluble  in  acetone.  The  absorption  spectrum 
of  the  nitrate  in  acetone  is  especially  characterized  by  the  weak  and  hazy 
appearance  of  the  bands. 

The  absorption  spectrum  of  neodymium  chloride  in  glycerol  is  more  like 
that  of  the  water  spectrum,  in  that  the  bands  are  often  very  sharp  and  narrow. 

The  absorption  spectra  of  the  chloride  and  nitrate  in  isobutyl  alcohol 
are  quite  different.  The  structure  and  distribution  of  the  intensity  of  the 
absorption  in  each  group  is  entirely  different.  The  center  of  gravity  of  the 
absorption  of  each  group  is  considerably  farther  to  the  red  in  the  case  of  the 
chloride,  but  the  composition  of  the  groups  is  so  different  for  the  two  salts 
that  no  relationship  can  be  seen  between  them  when  the  individual  bands  are 
compared.  These  solutions  would  afford  a  very  good  example  for  the  spectro- 
photography  of  chemical  actions  in  isobutyl  alcohol  at  low  temperatures. 

The  above  summary  is  made  simply  to  give  a  few  of  the  conclusions 
reached  in  previous  publications  from  this  laboratory  on  absorption  spectra, 
and  could  be  extended  almost  indefinitely.  As  the  subject  has  not  been  studied 
exhaustively,  it  is  only  given  as  typical  of  what  should  be  done  later.  In  the 
present  chapter  the  water,  methyl  and  ethyl  alcohols  and  glycerol  solutions 
were  not  taken  up.  For  a  further  treatment  the  reader  should  refer  to  the 
chapters  that  are  to  follow.  On  account  of  lack  of  time,  the  work  on  this 
subject  must  be  regarded  as  just  begun.  The  following  is  the  purpose  of  the 
investigation.  In  the  case  of  the  uranyl  bands  it  was  found  possible  in  many 
instances  to  trace  the  bands  by  gradual  changes  from  one  salt  to  another.  By 
this  means  it  was  hoped  to  study  chemical  reactions  in  various  solvents,  to 
find  if  a  chemical  reaction  had  the  same  effect  on  the  uranyl  bands  under 
different  conditions.  For  a  similar  reason  the  neodymium  spectrum  has  been 
broken  up  into  groups  of  bands,  and  it  was  proposed  to  study  these  minutely  as 
conditions  were  changed.  The  purpose  here  is  to  give  a  description  of  as  many 
characteristic  groups  as  possible,  and  to  correlate  the  groups  that  are  alike. 
It  might  be  assumed,  when  the  groups  were  constituted  of  the  same  bands  with 
the  same  relative  intensity,  sharpness,  etc.,  that  the  physical  and  chemical 
environment  of  the  absorbing  centers  was  the  same,  etc.  Much  more  work 
of  the  above  kind  remains  to  be  done,  especially  with  the  rare  earths  already 
described,  erbium,  holmium,  etc.  The  absorption  of  the  dry  salts,  the  phos- 
phorescent spectra,  and  the  absorption  spectra  at  low  temperatures  should 
be  obtained.  This,  naturally,  brings  us  to  the  subject  as  it  is  presented  in 
the  two  chapters  that  follow. 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  43 

THE  ABSORPTION   SPECTRUM    OF   SOLUTIONS  OF  CERTAIN    SALTS 
OF   URANIUM. 

For  a  full  discussion  of  the  absorption  spectrum  of  a  large  number  of 
uranium  solutions  the  reader  should  consult  Publication  No.  130  of  the  Car- 
negie Institution  of  Washington.  In  the  following  pages  only  a  few  solutions 
are  discussed,  these  being  for  the  most  part  solutions  of  the  uranyl  salts  in  some 
of  the  organic  solvents.  This  was  taken  up  because  corresponding  neodymium 
solutions  were  being  investigated,  and  it  was  thought  to  be  of  some  interest 
to  study  a  few  uranyl  solutions  in  the  same  way.  In  the  description  of  the 
bands  of  uranium  solutions  it  must  be  remembered  that  the  terms  wide,  fine, 
sharp,  narrow,  broad,  etc.,  are  relative  to  other  uranyl  or  uranous  bands 
and  not  to  neodymium  or  samarium  bands.  A  sharp  uranyl  band  would, 
therefore,  be  a  very  wide  and  hazy  neodymium  band. 

URANYL  CHLORIDE  IN  PROPYL  ALCOHOL. 

The  absorption  spectrum  of  uranyl  chloride  in  propyl  alcohol  is  given  in 
B,  plate  18.  The  absorption  bands  of  the  propyl  alcohol  solution  are  quite 
strong  and  appear  at  the  following  positions :  XX  3980, 4100,  4230,  about  4400 
(this  band  is  apparently  double),  4580,  4750,  and  4910.  The  upper  strip  shows 
quite  well  the  olifference  in  intensity  of  the  a  and  b  bands.  In  this  strip  the 
b  band  is  very  broad  and  strong,  running  from  X  4690  to  about  X  4820.  On 
the  other  hand,  the  a  band  is  quite  weak,  and  is  not  more  than  about  40 
Angstrom  units  in  width. 

URANYL  CHLORIDE  IN  ISOPROPYL  ALCOHOL. 

A,  plate  14,  gives  the  absorption  spectrum  of  uranyl  chloride  in  isopropyl 
alcohol.  The  blue-violet  band  is  seen  to  be  quite  prominent,  its  middle  coming 
at  about  X  4350,  about  100  Angstrom  units  farther  towards  the  red  than  for 
the  aqueous  solutions.  The  uranyl  bands  are  very  weak  and  diffuse,  being 
much  more  so  than  for  the  propyl  alcohol  solution.  The  a  band  does  not 
appear  on  the  spectrogram.  The  following  bands  show:  X  4100,  X  4250,  X  4360 
(these  two  bands  practically  merge  into  one  another),  X  4560,  and  X  4750. 

URANYL  CHLORIDE  IN  BUTYL  ALCOHOL. 

The  absorption  spectrum  of  uranyl  chloride  in  butyl  alcohol  is  given  in 
the  three  upper  strips  of  A,  plate  15.  It  will  be  seen  that  the  uranyl  bands  are 
very  wide  and  diffuse.  The  following  bands  can  be  distinguished  from  the  gen- 
eral absorption:  XX  3850,  3960,  4100,  4240,  4390,  4560,  4750,  4970.  The  bands 
are  all  very  diffuse,  the  last  band  being  about  150  Angstrom  units  in  width. 

URANYL  CHLORIDE  ix  ISOBUTYL  ALCOHOL. 

The  absorption  spectrum  of  uranyl  chloride  in  isobutyl  alcohol  is  given 
in  B,  plate  19.  The  spectrogram  gives  the  following  uranyl  bands:  XX 4400, 

4560,  4720,  and  4900. 

URANYL  CHLORIDE  IN  ETHER. 

The  following  uranyl  bands  have  been  photographed  for  a  solution  of 
uranyl  chloride  in  ether:  XX  4040,  4160,  4300,  4444,  and  4630.  The  solubility 
of  uranyl  chloride  in  dry  ether  is  very  small. 


44  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

URANYI,  CHLORIDE  IN  METHYL  ESTER. 

The  uranyl  bands  show  quite  strongly  in  the  methyl  ester  solution  of  the 
chloride.  The  bands  are  as  follows :  X  4030(0),  X  4160(/),  X  4280(e),  X  4440(d) 
(this  band  may  be  double  and  thus  really  represent  de  instead  of  simply  d  as 
given  above),  X  4620(c),  X  4790(6),  and  X  4920(a).  The  a  band  is  very  weak, 
compared  with  the  b  band.  Beyond  the  a  band  towards  the  red,  there  is  a 
very  weak  band  which  is  so  weak  that  it  is  very  difficult  to  distinguish  it  from 
the  absorption  of  the  blue-violet  band  itself. 

URANYL  CHLORIDE  IN  ETHYL  ESTER. 

B,  plate  14,  represents  the  absorption  spectrum  of  a  solution  of  uranyl 
chloride  in  ethyl  ester.  The  absorption  bands  are  very  strong  and  are  quite 
sharp.  The  wave-lengths  and  general  appearance  of  the  bands  are  practically 
the  same  as  that  of  the  methyl  ester  solution  previously  described. 

URANYL  CHLORIDE  IN  FORMAMIDE. 

B,  plate  15,  represents  the  absorption  of  a  solution  of  uranyl  chloride  in 
formamide.  The  uranyl  bands  appear  quite  strong,  especially  the  long  wave- 
length bands.  The  three  bands  in  the  second  strip  appear  of  about  equal  inten- 
sity at  X  4450,  X  4650,  and  X  4840.  The  latter  band  is  probably  the  6  band. 
The  a  band  does  not  appear  at  all  on  the  spectrogram. 

URANYL  NITRATE  IN  PROPYL  ALCOHOL. 

B,  plate  21,  represents  the  absorption  spectrum  of  uranyl  nitrate  in  propyl 
alcohol.  The  absorption  bands  are  quite  strong  and  sharp,  and  appear  as 
follows :  XX  3640,  3750,  3850,  3970,  4080,  4190,  4320,  4470,  4640,  and  4820.  The 
latter  band  is  probably  the  a  band,  as  it  is  very  much  narrower  than  the  band 
at  X  4640. 

URANYL  NITRATE  IN  ACETONE. 

The  photograph  of  the  absorption  spectrum  of  uranyl  nitrate  in  acetone 
showed  only  three  bands.  These  bands  were  quite  narrow,  but  were  not  as 
sharp  as  the  chloride  bands.  They  are  at  X  4510,  X  4660,  and  X  4830. 

URANYL  NITRATE  IN  METHYL  ESTER. 

The  absorption  spectra  of  uranyl  nitrate  in  methyl  ester  is  given  in  A, 
plate  15.  The  bands  are  rather  weak,  appearing  at  XX  3900,  4000,  4110,  4220, 
4340,  and  4480. 

URANOUS  CHLORIDE  IN  PROPYL  ALCOHOL. 

The  absorption  spectrum  of  uranous  chloride  in  propyl  alcohol  is  given  in 
A,  plate  18.  The  absorption  bands  are  all  quite  strong,  especially  the  uranyl 
bands.  The  uranyl  bands  shown  most  prominently  are  those  at  X  4590  and 
X  4750,  each  about  80  Angstrom  units  wide,  and  a  very  wide  band  at  X  4950 
about  150  Angstrom  units  wide.  Twoofine  bands  appear  at  about  X  5190  and 
X  5210.  These  bands  are  about  10  Angstrom  units  in  width.  A  band  at 
X  5500  is  about  120  Angstrom  units  in  width.  A  group  of  three  narrow  bands 
appears  at  about  X  5720,  X  5750,  and  X  5770.  The  middle  band  is  the  strongest 
one  of  the  group,  and  is  about  15  Angstrom  units  wide.  Absorption  maxima 
appear  at  about  X  6100,  X  6270,  and  X  6520.  This  whole  region  is  one  of  more 
or  less  general  absorption,  due  to  the  above  very  wide  bands.  The  band  at 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  45 

X  6720  is  very  similar  to  the  uranyl  bands  at  X  4590  and  X  4750.  The  general 
appearance  of  these  uranous  bands  in  the  red  is  very  much  like  that  of  the 
aqueous  uranous  bands. 

URAXOUS  CHLORIDE  IN  ISOBCJTYL  ALCOHOL. 

A,  plate  20,  represents  the  absorption  spectrum  of  uranous  chloride  in 
isobutyl  alcohol.     The  uranous  bands  of  this  absorption  spectrum  appear 
quite  sharp,  especially  when  they  are  broad,  as  is  the  case  in  the  upper  strips 
of  this  spectrogram.     The  first  strip  shows  a  double  band  at  about  X  4300. 
These  bands  practically  merge,  especially  in  the  other  strips,  the  shorter  wave- 
length band  being  much  more  intense.    Quite  a  sharp  band  appears  at  X  4950, 
with  a  broad  region  of  absorption  on  the  violet  side.    With  a  larger  amount 
of  salt  this  absorption  is  greatly  increased,  resulting  in  a  very  great  widening 
of  the  band  on  the  violet  side,  while  the  red  side  widens  but  little.    A  band 
appears  at  X  5480,  a  weak  band  at  X  6300,  a  strong  band  from  X  6400  to  X  6600, 
and  a  strong  band  at  X  6720.    The  spectrogram  shows  the  total  absence  of 
the  uranyl  bands,  and  very  slight  absorption  in  the  region  of  the  ultra-violet. 
The  upper  strip  shows  the  wide  uranous  bands  very  sharply  indeed. 

URANOUS  CHLORIDE  IN  METHYL  ESTER. 

B,  plate  24,  represents  the  absorption  spectrum  of  uranous  chloride  in 
methyl  ester.    From  the  absorption  spectrum  it  is  apparent  that  the  uranyl 
salt  has  been  largely  reduced,  since  the  uranyl  bands  do  not  show  at  all. 
Uranous  bands  appear  at  X  4300  (about  120  Angstrom  units  in  width).    There 
is  a  region  of  strong  absorption  extending  from  about  X  4700  to  X  5100,  with 
the  strongest  absorption  in  the  longer  wave-length  portion  of  this  region; 
resulting  in  a  much  greater  widening  of  the  band  towards  the  violet  as  the 
amount  of  jsalt  in  the  beam  of  light  is  increased.    There  is  a  band  at  X  5500 
about  150  Angstrom  units  wide  and  the  red  bands  appear.    The  red  bands  are 
both  rather  wide,  the  stronger  and  narrower  one  being  at  X  6730.     In  strip  3 
the  absorption  runs  from  X  6400  to  about  X  6760.    As  the  absorption  increases 
this  red  absorption  region  widens  very  unsymmetrically  towards  the  region 
of  shorter  wave-lengths.   This  solution,  like  most  other  clear  uranous  solutions, 
shows  very  little  general  absorption  in  certain  regions  of  the  spectrum.    Even 
the  general  absorption  in  the  ultra-violet  is  not  so  very  great.    When  a  large 
amount  of  the  solution  is  placed  in  the  beam  of  light,  considerable  light  still 
passes  through,  and  the  edges  of  the  absorption  bands  appear  quite  sharp. 

THE   ABSORPTION    CENTERS    OF   URANIUM    SPECTRA. 

Important  results  will  probably  be  obtained  by  a  study  of  uranyl  and 
uranous  compounds  at  low  temperatures.  It  might  be  possible  to  obtain 
aggregates  of  sufficient  size  to  be  seen  by  the  ultra-violet  microscope,  or  to  be 
observed  in  a  manner  somewhat  similar  to  that  of  the  scintillation  method  of 
observing  the  a  rays  on  a  phosphorescent  screen.  The  uranyl  aggregates  could 
be  illuminated  by  flashes  of  ultra-violet  light  and  by  proper  sector  arrange- 
ments the  aggregates  could  be  viewed  in  the  intervals  between  the  illumina- 
tion. These  aggregates  should  then  appear  as  centers  of  the  green  uranyl 
phosphorescence.  Neodymium  compounds  in  phosphorogens  could  possibly 
be  treated  in  the  same  manner.  These  salts  should  also  be  studied  when  under 


46  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

bombardment  by  /3  rays,  if  they  do  not  show  any  effect  by  a  rays.  Recent 
studies  of  phosphorescent  screens  subjected  to  a-ray  bombardment  has  led  to 
the  belief  that  these  substances  are  composed  of  aggregates. 

THE   ABSORPTION    SPECTRUM    OF    GADOLINIUM. 

Very  little  has  been  done  on  the  absorption  spectrum  of  gadolinium.  A 
dilute  nitrate  solution  in  a  10  mm.  layer  showed  several  weak  bands  at  X  3500 
to  X  3390,  with  a  maximum  at  X  3470.  A  weak  band  appeared  at  X  3300  to 
X  2890  and  continuous  absorption  commenced  at  about  X  2200.  According  to 
Soret  there  is  a  band  from  X  2800  to  X  2450. 

GADOLINIUM  CHLORIDE  IN  WATER. 

B,  plate  28,  shows  the  absorption  of  a  solution  of  gadolinium  chloride, 
1.407  normal;  the  depths  of  cell  starting  from  the  lowest  strip  being  2,  10,  15, 
22,  22,  and  100  mm.  The  spectrogram  shows  that  there  is  quite  a  strong, 
general  absorption  in  the  ultra-violet,  amounting  to  several  hundred  Ang- 
strom units  in  the  case  of  the  2  mm.  length  of  layer,  transmission  beginning 
at  about  X  2700.  For  the  100  mm.  length  of  layer  this  absorption  extends 
to  about  X  3700,  the  edge  of  the  transmission  being  very  broad. 

The  plate  shows,  besides  this  general  absorption,  two  very  sharp  bands  at 
X  2925  and  X  2980.  These  appear  clearly  for  the  10  mm.  layer.  For  the  100 
mm.  layer  a  weak  band,  about  25  Angstrom  units  in  width,  appears  at  X  3910. 
A  very  weak  band  appears  at  X  3970.  This  band  is  so  weak  that  it  can  hardly 
be  seen  in  the  original  film. 

GADOLINIUM  CHLORIDE  IN  ETHYL  ALCOHOL. 

Plate  28,  A,  gives  the  absorption  of  a  0.8  normal  solution  of  gadolinium 
chloride  in  ethyl  alcohol;  the  depths  of  cell,  starting  from  the  lowest  strip, 
being  2,  4,  9,  18,  27,  and  27  mm. 

One  of  the  most  pronounced  characteristics  of  the  absorption  of  this 
alcoholic  solution  is  the  enormous  absorption  in  the  ultra-violet,  compared 
with  the  aqueous  solution.  The  edge  of  this  absorption  is  very  diffuse.  It 
extends  to  about  X  3000  for  the  2  mm.  solution,  and  to  about  X  4400  for  the 
27  mm.  solution. 

The  only  characteristic  part  of  the  absorption  spectrum  is  a  very  diffuse 
band  at  X  4360.  This  band  is  gradually  included  in  the  region  of  general 
absorption,  as  the  depth  of  cell  is  increased. 

It  will  be  noticed  that  the  absorption  spectra  of  the  alcohol  and  aqueous 
solutions  are  very  different  indeed. 

THE  ABSORPTION    SPECTRUM    OF   DYSPROSIUM. 

Very  little  work  has  been  published  on  the  absorption  spectrum  of  dyspro- 
sium. Lecoq  de  Boisbaudran1  has  described  the  following  bands  arranged 
according  to  the  intensity  of  the  bands:  Dya,  X  =  4515;  Dy@,  X  =  4750;  Dyy, 
X  =  7565;  Dy8,  X  =  4275. 

Urbain2  has  observed  only  X  4740  and  a  weak  band  at  X  4530  to  X  4500. 

'  Compt.  Rend.,  102,  1005  (1886).  z  Ann.  Chim.  Phys.,  19,  244  (1900). 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS.  47 

DYSPROSIUM  CHLORIDE  IN  WATER. 

The  absorption  spectrum  of  aqueous  solutions  of  dysprosium  chloride  is 
given  in  B,  plate  29,  and  A,  plate  30.  The  absorption  in  the  ultra-violet  is 
very  small  for  aqueous  solutions  of  dysprosium  chloride,  even  when  the 
depth  of  cell  is  as  great  as  21  mm.,  and  the  concentration  is  1.86  normal,  as 
it  is  for  the  last  strip  of  A,  plate  30. 

Strip  2,  B,  plate  29,  represents  the  absorption  of  a  6  mm.  layer  of  1.86 
normal  concentration.  As  this  strip  shows  many  of  the  bands,  it  will  be 
described  in  detail.  The  general  appearance  of  the  bands  is  much  the  same, 
although  they  vary  greatly  in  intensity.  The  edges  are  quite  sharp,  although 
none  of  the  bands  are  as  sharp  and  clear  as  the  neodymium  water  band, 
X4271. 

The  first  band  observed  in  the  ultra-violet  is  X  3130.  As  will  be  seen  from 
the  spectrograms  the  bands  in  the  ultra-violet  are  by  far  the  strongest 
in  the  spectrum.  X  3130  is  one  of  the  strongest  of  these  ultra-violet  bands, 
and  is  about  40  Angstrom  units  wide.  The  next  band  at  X  3260  is  about  20 
Angstrom  units  wide  and  is  quite  weak.  It  is  very  similar  and  of  the  same 
order  of  intensity  as  the  bands  at  XX  3470,  3670,  3690,  3800,  3850,  4170,  4340, 
4400,  and  4430.  Of  these  bands,  the  latter  two  are  the  strongest.  The  band 
X  3390  is  the  strongest  oband  in  the  whole  spectrum.  It  possesses  sharp 
edges  and  is  over  50  Angstrom  units  in  width,  while  the  strong  band 
X  3535  has  only  a  width  of  30  Angstrom  units.  The  band  X  3760  is  also  quite 
strong  and  has  a  width  of  about  25  Angstrom  units.  Other  bands  appear 
faintly  at  XX  4650,  5300,  and  6350,  but  these  are  so  weak  that  their  positions 
can  hardly  be  measured.  The  band  at  X  3970  is  very  broad  and  weak,  and 
shows  best  in  the  fifth  strip. 

In  the  last  strip  of  100  mm.  depth,  quite  a  number  of  new  bands  appear. 
The  ultra-violet  absorption  has  become  so  strong  that  the  whole  region  to 
X4050  is  absorbed.  The  band  at  X 41 60  is  apparently  double,  being  much  more 
intense  on  the  violet  side.  The  bands  at  X4190  and  X4220  are  much  weaker, 
the  former  almost  merging  into  X4160.  Absorption  bands  extend  from  X  4250 
to  X  4300,  X  4450  to  X  4580,  X  4680  to  X  4820.  Very  weak  bands  appear  at 
XX  4840,  4890,  4930,  4960,  5425,  5460,  5490,  5520,  6460,  6570,  and  6600.  The 
band  X  5380  is  quite  strong  and  almost  merges  into  the  other  bands  in  this 
region.  The  band  X  6440  is  also  quite  strong.  X  6440  and  X  6460  are  very 
diffuse  and  almost  form  a  single  band. 

DYSPROSIUM  CHLORIDE  IN  METHYL  ALCOHOL. 

The  absorption  spectrum  of  a  solution  of  dysprosium  chloride  in  methyl 
alcohol  is  given  in  A,  plate  29.  The  absorption  is  greater  for  the  alcohol 
solution,  especially  the  general  ultra-violet  absorption.  Otherwise  the  relative 
intensity,  number,  wave-length,  and  general  appearance  of  the  absorption 
bands  are  exactly  the  same  as  the  bands  of  the  aqueous  solution. 

DYSPROSIUM  CHLORIDE  IN  ETHYL  ALCOHOL. 

With  the  exception  of  the  very  much  greater  ultra-violet  absorption,  the 
spectra  of  dysprosium  chloride  in  water,  methyl  alcohol,  and  ethyl  alcohol  (B, 
plate  31)  are  very  much  the  same;  the  ethyl  alcohol  band  at  X  5400  being  wider 
and  of  greater  wave-length  than  the  water  and  methyl  alcohol  bands  at  X  5380. 


48  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

The  fact  that  this  one  band  should  appear  of  a  different  wave-length  in 
ethyl  alcohol,  as  compared  with  water,  while  the  other  dysprosium  bands  appear 
to  be  the  same  for  both  solvents,  might  be  taken  to  indicate  that  this  band 
was  not  due  to  dysprosium.  A  difference  of  this  kind  might  lead  to  a  possible 
method  of  ascertaining  the  presence  of  the  salts  of  two  different  elements  in 
solution.  In  the  case  of  neodymium  salts  it  was  found,  in  general,  that  if  one 
solvent  had  one  characteristic  band,  all  the  solvent  bands  were  more  or  less 
characteristic.  On  the  other  hand,  it  must  be  remembered  that  in  the  case 
of  the  uranyl  bands  the  differences  for  different  solvents  were  usually  much 
greater  for  the  longer  wave-length  bands.  So,  in  the  above  case  of  dysprosium 
chloride  in  ethyl  alcohol,  we  may  assume  that  the  band  X  5380  may  not  be 
due  to  dysprosium.  It  may  be  possible  that  the  difference  in  the  action  of 
acids  on  the  bands  of  the  spectra  of  a  given  salt,  or  the  difference  of  the  spectra 
as  obtained  with  the  same  salt  in  different  solvents,  may  be  useful  in  separating 
the  different  elements. 

DYSPROSIUM  ACETATE  IN  WATER. 

The  absorption  spectrum  of  dysprosium  acetate  (0.4  normal)  in  water  is 
given  in  A,  plate  31.  The  depths  of  cell  were  4, 16,  25  and  34  mm.  The  spec- 
trum is  very  similar  to  that  of  the  aqueous  solution  of  the  chloride.  The  bands 
are,  however,  somewhat  more  diffuse.  The  wave-lengths  of  the  bands,  while 
comparatively  weak,  appear  to  be  the  same  for  the  chloride  and  the  acetate. 
The  acetate  bands  widen  more  to  the  red,  so  that  when  the  bands  are 
quite  wide,  the  acetate  bands  appear  to  be  relatively  shifted  towards  the 
red.  The  addition  of  concentrated  nitric  acid  produces  little  effect  on  the 
wave-length,  or  the  appearance  of  the  dysprosium  acetate  bands  in  water. 

THE    ABSORPTION    SPECTRUM    OF    SAMARIUM. 

The  absorption  spectrum  of  samarium  has  been  studied  much  more  exten- 
sively than  that  of  gadolinium  and  dysprosium.  On  the  following  page  is  a 
table  giving  the  wave-lengths  of  some  of  the  bands  as  determined  by  various 
observers. 

In  general  appearance  the  absorption  spectra  of  samarium  salts  are  very 
similar  to  those  of  the  dysprosium  salts,  the  strong  bands  of  the  spectrum 
being  located  in  approximately  the  same  violet  and  ultra-violet  part  of  the 
spectrum.  The  general  appearance  of  the  individual  bands  is  very  similar 
to  that  of  the  dysprosium  bands,  the  samarium  bands  being,  however,  some- 
what narrower  and  having  sharper  edges. 

SAMARIUM  CHLORIDE  IN  WATER. 

The  absorption  spectrum  of  samarium  chloride  in  water  is  shown  in  A, 
plate  32.  The  concentration  is  1.31  normal  and  the  depths  of  cell,  starting 
from  the  lowest  strip,  are  2,  6,  12,  16,  20,  and  100  mm. 

From  the  spectrogram  it  is  seen  that  for  the  aqueous  solution  the  ultra- 
violet absorption  is  very  small  indeed.  A  weak  and  apparently  quite  wide 
band  appears  at  about  X  3050.  For  the  6  mm.  depth  of  cell,  second  strip,  bands 
appear  at  XX  3200,  3320,  3510,  3630,  3910,  etc.  The  other  bands  are  quite 
weak  and  will  be  given  for  the  20  mm.  layer.  Of  the  above  bands,  the  X  3910 
is  by  far  the  strongest  of  all  the  samarium  bands.  For  the  20  mm.  layer  the 
following  bands  appear:  X  3420  (diffuse,  about  20  Angstrom  units  wide),  X  3470 


MAPPING    ABSORPTION    SPECTRA    OF    VARIOUS    SALTS. 


49 


to  X  3540,  X  3550  very  weak,  X  3570  very  weak,  X  3600  to  X  3660,  X  3720  very 
weak  and  wide,  X  3770  weak,  X  3800  (about  20  Angstrom  units  wide),  X  3860 
to  X  3945,  X  3970,  X  4050,  X  4070,  X  4320  very  wide  and  weak,  X  4540  (about 
40  Angstrom  units  wide) ;  X  4640  to  X  4750  is  a  region  consisting  of  two  diffuse 
bands  that  practically  run  together,  X  4800  weak,  X  5110  weak.  Other  bands 
appear  in  the  region  of  longer  wave-lengths,  but  they  are  very  weak. 

A  100-mm.  strip  showed  complete  absorption  of  wave-lengths  shorter 
than  X  4130.  Bands  appeared  from  X  4210  to  X  4370;  a  band  about  30  Ang- 
strom units  wide  at  X  4420;  a  band  from  X  4470  to  X  4840,  X  4890  to  X  4950, 
X  4200,  X  4230  (these  two  bands  are  of  about  the  same  intensity,  rather  dif- 
fuse and  about  20  Angstrom  units  wide),  X  5500,  X  5525;  these  bands  are  very 
similar  to  the  preceding  pair,  being,  however,  considerably  more  intense. 


Lecoq  de 
Boisbandran.1 

Soret. 

Thalen.z 

Kriiss  and 
Nilson. 

Bettendorf. 

Forsling.' 

Bahm..      D— 

For- 
manek.* 

5590 

5590 

5590-5560 

5587 

5590-5582 

5600 

5590 

5588 

....       !  5290 

5282 

5010-5000 

5000 

5015^4970 

5004 

5039^4995 

5o6i 

4980 

5211 

4890 

4890 

4891 

.... 

5005 

4860-4740 

4800 

486O4'720 

4830-4750 

4885^4736 

4804^4783 

4800      !  !  !  ! 

4892 

4761^727 

4760 

4880 

4640-4630 

4635 

4660-4600 

4633 

4690-4619 

4632 

4625         4630 

4750 

.... 

4530 

4634 

4450^-4370 

4443-4383 

4430 

4530 

4i70 

4190-4150 

4185-4150 

4174 

4220-4151 

4174 

4165         4170 

4436 

4157 

4175 

4080^4060 

4090 

4090 

4083 

.... 

4077 

.'.'.'.         4070 

4035-4030 

4020 

4090 

4007  .'5 

4016-4007 

.... 

3942-3932 

3906 

3900 

3760^-3720 

3752-3742 

3750-3730    3750 

3738-3732 

364(K3600 

3630-3615 

3640-3600    3620 

i  Spectres  Lumineux,  Paris  bei  Gauthier-Villars  (1874). 

*  Journ.  de  Phys.,  2,  446  (1883). 

•Bih.  K.  Svensk.Vet.-Ak.  Handl.,  28,  n.  Nr.  1  (1902). 


<Zeit.  angew.  Chemie.,  15,  1282  (1902). 
6  Die  qualitative  Spectralanalyse  anorganischer  Korper, 
Berlin  bei  Muckenberger  (1900). 


SAMARIUM  NITRATE  IN  WATER. 

The  absorption  spectrum  of  samarium  nitrate  in  water  is  given  in  A, 
plate  33.  The  absorption  bands  have  almost  the  same  characteristics,  rela- 
tive intensity,  wave-lengths,  etc.,  that  water-bands  of  samarium  chloride  have. 

SAMARIUM  CHLORIDE  IN  METHYL  AND  ETHYL  ALCOHOLS. 

The  absorption  spectrum  of  samarium  chloride  in  methyl  alcohol,  B, 
plate  32,  is  so  similar  to  the  absorption  of  this  salt  in  ethyl  alcohol,  A,  plate 
34,  that  only  the  former  will  be  described  in  detail.  It  will  be  seen  from  the 
spectrograms  that  the  general  absorption  in  the  ultra-violet  and  violet  in 
the  case  of  the  ethyl  alcohol  solution  is  very  much  greater  than  in  the  case 
of  the  methyl  alcohol  solution. 

B,  plate  32,  represents  the  absorption  of  a  normal  solution  of  sama- 
rium chloride  in  methyl  alcohol,  the  depths  of  all  being  2,  5,  9,  18,  27,  and 
27  mm.  The  last  spark  spectrum  was  taken  with  the  solution  removed  simply 
4 


50  THE    ABSORPTION    SPECTRA    OP    SOLUTIONS. 

for  the  purpose  of  making  wave-length  measurements.  The  first  strip  shows 
the  following  bands:  X  3200,  X  3330,  X  3500,  X  3540,  X  3640,  X  3910,  X3925, 
and  some  weaker  bands  farther  towards  the  red.  The  third  strip  shows  the 
following  bands:  X  3200  quite  weak;  X  3330,  X  3350,  X  3430,  and  X  3450  very 
weak  and  diffuse,  appearing  almost  as  a  single  band;  X  3500,  X  3540,  X  3570, 
X  3640;  X  3910,  the  strongest  band  in  the  spectrum,  is  about  35  Angstrom 
units  wide,  X  3950  about  10  Angstrom  units  wide,  X  3970  about  6  Angstrom 
units  wide,  X  4060  and  X  4100  are  each  about  30  Angstrom  units  wide  and  quite 
weak.  Other  bands  are  easy  to  see  and  will  be  described  in  the  last  strip.  In 
this  strip  the  ultra-violet  absorption  is  complete  to  X  3350.  In  addition  to 
the  bands  mentioned  above  there  were  bands  at  XX  4290  weak,  4310  weak, 
4350  weak,  4410  weak,  4520,  4545,  4570;  this  triple  group  is  perfectly  sym- 
metrical, the  middle  band  being  much  the  strongest;  4650,  4705,  and  4760 
are  each  about  40  Angstrom  units  wide,  are  diffuse  and  weak  with  the  middle 
band  having  the  greatest  intensity;  4810  is  about  10  Angstrom  units  in  width, 
4920  quite  weak  and  diffuse,  and  5200  is  very  weak.  No  other  bands  in  the 
longer  wave-length  region  are  visible  in  addition  to  those  described. 

SAMARIUM  CHLORIDE  IN  WATER  AND  ETHYL  ALCOHOL. 

The  absorption  spectra  of  samarium  chloride  in  mixtures  of  water  and 
ethyl  alcohol  are  given  in  B,  plate  33,  and  B,  plate  34.  The  change  from  the 
alcohol  to  the  water  spectrum  can  easily  be  seen  in  the  shift  of  the  bands  of 
strip  1  compared  with  strip  2  in  B,  plate  34.  The  very  great  persistency  of 
the  water  bands  is  shown,  since  in  this  case  (strip  2)  only  about  5  per  cent 
of  water  is  present.  The  band  X  3970  seems  to  be  a  characteristic  water  band. 
In  strip  1,  B,  plate  33,  this  band  does  not  appear,  but  in  strip  2  it  can  be 
clearly  seen  and  in  the  succeeding  strips  it  becomes  stronger.  It  seems,  there- 
fore, that  the  samarium  bands  behave  in  the  same  way  as  the  neodymium 
bands,  although  there  is  no  single  band  that  shows  the  effect  as  clearly  as  the 
neodymium  X  4271  water  band,  and  the  corresponding  X  4290  alcohol  band. 
Since  the  water  bands  are  so  persistent  it  would  be  very  interesting  to  carry 
this  work  to  temperatures  almost  as  low  as  the  freezing-point  of  alcohol.  In 
general,  a  lowering  of  temperature  has  increased  the  persistency  of  the  water 
bands. 


CHAPTER   IV. 


SPECTROPHOTOGRAPHY  OF  CHEMICAL  REACTIONS. 

INTRODUCTION. 

Prior  to  these  investigations,  very  little  work  had  been  done  on  the  effects 
produced  on  the  absorption  spectrum  of  a  salt  in  solution  when  acids  and 
various  other  reagents  that  produce  chemical  reactions  were  added.  Indeed, 
much  of  our  knowledge  of  what  is  in  solution  is  obtained  indirectly  rather  than 
by  a  direct  knowledge  of  the  composition  of  compounds  while  in  solution.  Con- 
siderable work  on  the  effect  of  the  introduction  of  certain  radicals,  groups,  etc., 
on  the  absorption  spectra  of  organic  compounds  has  been  done,  and  a  fairly 
complete  survey  of  this  work  is  given  in  the  first  chapter.  Especial  efforts 
have  been  made  to  discuss,  as  completely  as  possible,  our  knowledge  of  the 
absorbing  and  emitting  centers  of  light  and  heat. 

It  is  true  that  a  few  observers  had  noticed  that  in  some  cases  different 
salts  had  bands  of  different  wave-lengths,  when  dissolved  in  the  same  solvent. 
A  typical  example  of  this  kind  is  given  in  the  following  table.  Then  again, 
observers  had  noted  that  the  bands  of  one  salt  of  a  metal  were  finer  and 
sharper  than  the  bands  of  another  salt  (for  example,  neodymium  chloride  as 
compared  with  the  nitrate  in  water),  but,  as  far  as  we  know,  no  effort  has 
been  made  to  study  what  changes  in  the  bands  resulted  as  one  salt  of  a  metal 
was  changed  into  another  salt. 

The  following  table  gives  the  absorption  bands  of  some  double  acetates 
of  uranyl  according  to  Morton  and  Bolton:2 


NH4  
Ba  
Co 

4620 
|  4625 
4625  i 

4455 
4465 
4465 

4310  i 
4330  i 
4335 

4200 
4200 
4200 

4075 
4075 
4080 

K  
Li 

4625  ; 
4620  ! 

4460 
4455 

4320  i 
4320 

4200 
4205 

4070 
4080 

Mg  

4627  ! 

4480 

4337 

4215 

4085 

Na  
Rb. 

4620  ! 
4625  ; 

4453 
4465 

4310 
4315 

4185 
4202 

4055 
4080 

Sr  

4627  ! 

4480 

4335 

4205 

4075 

Tl  .. 

....  1  4640 

4480 

4320 

4205 

4085 

Zn 

4655 

4490 

4340 

4325 

4100 

|  ^  •"*  | 

For  the  following  double  sulphates  they  give : 


Ammonium  uranyl  sulphate  
Ammonium  diuranyl  sulphate  .... 
Magnesium  uranyl  sulphate 

4935 

4875 

4800 
4720 
4790 

4620 
4575 
4540 

4450 
4480 
4370 

4330J 
4330 
4230  ; 

4240 
4210 
4100 

Potassium  uranyl  sulphate 

4790 

4540 

4370 

4230  i 

4100 

Rubidium  uranyl  sulphate  
Thallium  uranyl  sulphate.  . 

4885 
4905 

4805 
4630 

4645 
4480 

4475 
4295 

4325 

4205 

Sodium  uranyl  sulphate  

4875 

4775 

4580 

4440 

4335  j 

4180 

1  Publication  130,  Carnegie  Institution  of  Washington. 
H'hem.  News,  28,  47,  113,  164,  233,  244,  257,  268  (1873). 


.-,1 


52  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

One  of  the  purposes  of  the  present  research  is  to  study  one  group  of 
bands  throughout  a  long  series  of  reactions.  The  first  group  of  bands  to  be 
studied  in  this  way  was  the  uranyl  bands.  Although  not  completely  followed, 
and  not  identified  with  certainty  in  every  case,  yet  for  aqueous  solutions,  at 
least,  it  has  been  possible  to  designate  these  bands  as  a,  6,  c,  d  ....  and  to 
follow  each  band  as  the  salt  is  changed  from  acetate  to  nitrate,  from  nitrate 
to  chloride,  from  chloride  to  sulphate,  etc.  It  is  found  in  all  these  changes 
that  the  individual  uranyl  bands  undergo  a  gradual  shifting  of  their  position 
in  the  spectrum.  Various  chemical  changes  have  been  accompanied  by  charac- 
teristic changes  in  the  absorption  spectrum;  e.g.,  a  narrowing  of  the  bands,  a 
shifting  of  the  bands  to  the  violet,  etc.  It  is  natural  to  try  to  correlate  as 
many  of  these  characteristics  as  possible,  but  as  yet  not  enough  work  has 
been  done  to  furnish  many  generalizations.  It  may  be  said,  qualitatively,  that 
in  many  instances  a  shifting  of  the  bands  towards  the  violet  is  often  accom- 
panied by  a  narrowing  and  sharpening  of  the  edges  of  the  bands.  This  is  a 
general  characteristic  also  of  the  temperature  effect,  since  a  lowering  of  the 
temperature  of  an  absorbing  compound  is  nearly  always  accompanied  by  a 
narrowing  of  the  absorption  bands  and  a  slight  shifting  towards  the  violet. 

Again,  it  is  natural  to  inquire  whether  the  same  chemical  reaction  produces 
the  same  changes  in  the  absorption  spectra  when  this  reaction  takes  place 
in  different  solvents.  Unfortunately  there  are  not  many  examples  of  this 
kind  that  can  be  tested.  In  general,  the  absorption  bands  of  different  salts 
in  the  same  solvent  are  practically  the  same,  so  that  a  chemical  reaction 
can  not  be  photographed  spectroscopically.  It  was  for  this  reason  that  a 
considerable  number  of  absorption  spectra  have  been  mapped.  A  number 
of  solvents  showing  a  difference  in  the  absorption  spectra  of  different  salts 
are  not  suited  very  well  for  this  kind  of  work.  Some  very  good  examples, 
however,  have  been  found,  and  these  will  soon  be  studied.  Acetone  was 
found  to  give  a  greater  difference  between  the  absorption  spectra  of  uranyl 
nitrate  and  the  other  uranyl  salts  than  water;  and  as  the  uranyl  acetone 
bands  are  very  sharp  and  these  solutions  can  be  studied  at  very  low  temper- 
atures, this  solvent  offers  exceptional  advantages  for  making  a  comparison 
between  the  same  chemical  reactions  in  the  two  solvents. 

The  closely  related  problem  as  to  whether  apparently  similar  chemical 
reactions  for  different  salts  in  the  same  solvent  are  really  similar  has  already 
been  answered  in  some  cases  in  the  negative.  We  have  seen  that  the  chem- 
ical reaction  that  takes  place  when  uranyl  chloride  is  changed  to  uranyl 
nitrate  has  resulted  in  a  narrowing  and  sharpening  of  the  uranyl  bands, 
and  a  gradual  shifting  of  these  bands  towards  the  violet.  The  same  reaction 
of  neodymium  chloride  to  neodymium  nitrate  in  water  results  in  the  bands 
being  made  broader  and  more  diffuse,  and  in  some  cases  these  bands  are 
slightly  shifted  towards  the  red. 

It  must  be  stated  that  the  study  of  the  changes  that  take  place  in  the 
neodymium  bands  has  been  too  complicated  for  the  present  research.  No 
other  element  shows  such  an  extremely  wide  diversity  in  the  structure  of  its 
various  groups  of  bands,  and  at  present  no  examples  have  been  found  where 
any  bands  can  be  traced  throughout  chemical  reactions.  The  changes  seem 
rather  to  be  connected  with  a  change  in  the  relative  intensity  of  bands  in  the 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS.  53 

same  group,  and,  therefore,  a  shifting  of  the  center  of  gravity  of  the  absorp- 
tion of  the  group  itself.  This  may  be  true  also  of  the  uranyl  bands,  since  it  is 
known  that  the  uranyl  bands  break  up  into  much  finer  bands  at  low  tempera- 
tures. At  any  rate,  the  changes  in  the  uranyl  bands  at  ordinary  tempera- 
tures, when  chemical  reactions  take  place,  are  comparatively  simple  compared 
with  the  same  changes  in  the  case  of  the  neodymium  bands. 

It  is  very  important  that  a  careful  study  be  made  of  a  series  of  chemical 
transformations  of  neodymium  salts  (especially  at  low  temperatures).  For 
instance,  it  has  been  shown  that  different  anhydrous  neodymium  salts  pos- 
sess very  different  absorption  spectra.  Comparisons  between  the  spectro- 
photographs  of  dry  chemical  reactions  should  be  made  and  these  compared 
with  the  same  reactions  in  various  solvents.  As  soon  as  we  know  what 
physical  and  chemical  conditions  are  connected  with  given  spectroscopic 
changes,  then  a  study  of  the  absorption  spectra  of  crystals  should  be  of  aid 
in  giving  us  an  insight  into  the  physical  and  chemical  conditions  within 
crystals.  An  example  of  this  kind  of  study  might  be  found  in  the  different 
varieties  of  ice.  Tammann1  has  shown  that  there  are  four  distinct  varieties, 
ice  i  and  iv  being  lighter  than  water,  and  ice  n  and  in  being  denser. 
According  to  Tammann  the  latter  two  varieties  are  composed  of  the  simpler 
molecules.  These  different  forms  of  ice  are  produced  at  different  tempera- 
tures and  pressures.  The  freezing-point  of  ice  I  is 

1°         -5.53°         -10.42°         -15.66° 

p  675  1141  1597  kg./cm.* 

Whereas  ice  in  is  formed  by  compressing  to  3000  kg./cm.2  and  cooling 
to  —80°,  ice  ii  is  formed  by  cooling  to  —80°  and  then  compressing  to  2700 
kg./cm.2  Ice  iv  is  probably  identical  with  the  tetragonal  ice  observed  by 
E.  Nordenskiold2  or  with  the  regular  ice  crystals  formed  from  75  per  cent  alco- 
holic solutions.3  The  absorption  spectra  of  colored  salts  like  those  of  neodym- 
ium, samarium,  or  uranium  would  probably  aid  in  a  study  of  these  different 
crystalline  types. 

Another  subject  that  seems  to  be  of  interest  and  promise  is  the  possibility 
of  breaking  up  absorption  spectra  into  related  groups.  The  work  of  Wood  on 
sodium  vapor  has  been  very  successful  in  this  respect,  each  monochromatic 
stimulating  wave-length  exciting  a  certain  resonating  system  within  the  atom 
or  molecule,  the  resultant  resonance  spectrum  including  light  of  the  same 
wave-length  as  that  of  the  exciting  light. 

Among  the  rare  earth  elements  praseodymium,  neodymium,  samarium, 
europium,  terbium,  dysprosium,  and  erbium  show  characteristic  absorption 
spectra  in  the  visible  wave-lengths,  and  also  are  examples  of  excellent  phos- 
phorogens.  Lanthanum,  gadolinium,  and  yttrium  do  not  possess  absorption 
spectra,  and  only  act  as  diluents.  Following  are  some  tables  given  by  Urbain 
of  the  various  phosphorescent  spectra  studied  by  him : 

1  Zeit.  phys.  Chem.,  72,  609  (1910). 

2  Ann.  d.  Phys.,  114,  612  (1861). 

3  Barendrecht:  Zeit.  phvs.  Chem.,  20,  240  (1896). 


54 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


PHOSPHORESCENCE  OF  PRASEODYMIUM,  NEODYMIUM,  AND  ERBIUM  IN  CALCIUM  OXIDE. 


Praseodymium. 

Neodymium.            Erbium. 

4875  vs. 

3920  s.          4040  w. 

4905  w. 

3980  s.           4045  w. 

4940  m. 

3640  to  4130      4060  w. 

4985  to  5030  vw. 

4190  sn.          4085  s. 

5090  to  5130  vw. 

4220  sn.          4095  m. 

5170  m.  dif. 

4230  sn. 

4460  m. 

5225  to  5280  vw. 

4270 

4520  m. 

5335  to  5370  w. 

4295  vs. 

4550  s. 

5527  w. 

4400  w. 

4590  s. 

5560  to  5600  w. 

4515  w. 

4620  w. 

5790  w. 

4575  s. 

4670  m. 

6045  s. 

4610  w. 

4690  m. 

6065  s. 

4660 

4730  w. 

6130  to  6220 

4690  w 

4760  m. 

6260  vs 

4785  w. 

6340  s. 

5270  to  5355  m. 

6670  to  6800  dif. 

5495  to  5550  w. 

5595  to  5630  m. 

vs.  =  very  strong;    w.  =  weak;    m.=  medium;  dif.  =  diffuse;    vw.  =  very 
weak;  s.  =  strong;  sn.=strong  and  narrow. 

The  phosphorescence  of  compounds  of  the  rare  earths  in  other  diluents 
is  much  simpler  than  in  calcium  oxide : 

PHOSPHORESCENCE  OF  PRASEODYMIUM  IN  CALCIUM  SULPHATE. 
XX  5876,  6000,  and  6100. 

PHOSPHORESCENCE  OF  ERBIUM  IN  CALCIUM  SULPHATE. 
XX  5220,  5435,  5535. 

PHOSPHORESCENCE  OF  ERBIUM  IN  CALCIUM  FLUORIDE. 
XX  5170,  5200,  5250,  5310,  5400,  5465  strong,  5510  strong,  5620. 

By  using  monochromatic  light  or  homogeneous  cathode  rays  of  different 
velocities,  it  might  be  possible  to  excite  only  certain  related  bands  and  not 
the  whole  absorption  spectrum.  This  might  apply  especially  to  the  uranium 
salts.  On  the  other  hand,  the  presence  of  the  diluent  might  preclude  any 
possibility  of  this  kind.  The  recent  work  of  Wood  and  Franck1  on  the  effect 
of  the  presence  of  helium  on  the  resonance  of  iodine  vapor  would  lead  to  a 
conclusion  of  this  kind.  A  study  of  the  fluorescence  of  sodium,  potassium, 
mercury,  and  iodine  vapor  shows  that  the  intensity  of  the  emitted  light  is 
greatly  reduced  if  air  or  some  other  inert  gas  is  present.  The  effectiveness 
of  a  gas  in  destroying  fluorescence  appears  to  increase  with  the  molecular 
weight.  In  the  case  of  the  fluorescence  of  anthracene,  Elston  found  that  hydro- 
gen and  nitrogen  had  very  little  effect,  while  oxygen  and  carbon  dioxide  had 
a  very  great  effect. 

Warburg2  has  shown  that  the  current  obtained  from  the  negative  point 
discharge  is  much  greater  in  nitrogen,  helium,  argon,  and  hydrogen  when  the 
last  traces  of  oxygen3  have  been  removed.  To  explain  this  Warburg  assumed 

1  Phil.  Mag.,  21,  309,  314  (1910). 

2  Ann.  d.  Phys.,  40,  1  (1896). 

3  J.  Franck:  Verb,  der  deutsch.  phys.  Ges.,  July  (1910). 


SPECTROPHOTOGRAPHY    OP    CHEMICAL    REACTIONS.  55 

that  the  mobility  of  the  negative  ions  in  the  pure  gases  was  much  greater 
than  when  traces  of  oxygen  were  present.  In  other  words,  the  electrons 
existed  largely  in  a  free  condition,  and  as  soon  as  oxygen  was  introduced,  the 
electrons  and  negative  ions  were  supposed  to  condense  on  the  oxygen  mole- 
cules. Small  traces  of  the  less  electro-negative  gases  are  found  to  act  in  the 
same  way.  Similarly,  Franck  and  Wood  believe  that  the  more  electro-nega- 
tive elements  have  a  greater  power  to  destroy  fluorescence,  and  this  agrees 
with  the  relative  destructive  power  as  given  by  the  series  hydrogen,  air,  car- 
bon dioxide,  and  ether  vapor,  the  latter  having  the  greatest  effect.  The  con- 
clusion reached  is  that  the  gases  that  interfere  with  the  motions  of  the  free 
electrons  are  also  the  ones  that  modify  the  motion  of  the  bound  electrons 
to  the  greatest  extent.  In  this  connection  the  influence  of  the  presence  of 
helium,  argon,  nitrogen,  oxygen,  and  chlorine  on  the  fluorescence  of  mercury 
and  iodine  has  been  studied. 

According  to  Lorentz's  hypothesis  that  the  damping  results  from  col- 
lisions, the  damping  factor  would  be  a  function  of  the  molecular  weight.  On 
the  other  hand,  the  destructive  effect  of  helium  on  the  fluorescence  of  iodine 
is  much  less  than  that  of  hydrogen,  the  effects  due  to  hydrogen  and  argon 
being  about  the  same,  although  the  molecular  weight  of  the  latter  is  forty 
times  as  great  as  the  former.  The  gas  having  the  greatest  effect  is  chlorine, 
and  next  to  it  ether.  It  therefore  seems  that  the  power  of  a  gas  to  combine 
with  electrons  is  a  very  important  factor  in  determining  the  role  which  that 
gas  will  play  in  the  suppression  of  fluorescence. 

The  fact  that  the  maximum  intensity  of  fluorescence  in  a  pure  gas  occurs 
at  different  pressures  for  different  gases  may  also  be  explained  on  the  above 
hypothesis.  To  obtain  visible  fluorescence  there  must  be  a  sufficient  number 
of  molecules  present  to  give  a  certain  intensity  of  the  emitted  light,  but  this 
number  of  molecules  must  not  be  so  great  as  to  disturb  each  other.  In  a 
strongly  electro-negative  gas  the  vibration  of  electrons  in  one  molecule  will 
be  influenced  by  the  presence  of  other  molecules  in  the  neighborhood,  so  that 
for  a  gas  like  bromine  the  fluorescence  would  be  expected  to  take  place  at  much 
lower  pressures  than  is  the  case  for  a  much  less  electro-negative  gas  like 
iodine;  while  in  the  case  of  mercury  the  pressure  would  be  very  much  greater. 
This  has  been  found  to  be  the  case. 

In  treating  the  following  cases  of  chemical  reactions,  the  theory  of  aggre- 
gates, as  fully  developed  in  the  general  remarks  at  the  end  of  this  monograph, 
will  be  assumed.  It  may  be  possible  to  obtain  some  knowledge  of  these  aggre- 
gates by  other  methods.  In  the  study  of  a,  0,  and  7  rays  it  is  found  that,  in 
general,  the  absorption  of  these  radiations  depends  on  the  atomic  structure 
of  the  matter  they  traverse,  rather  than  on  the  molecular  structure.  There 
may  possibly  be  some  exceptions  to  this  rule.  For  instance,  uranium  and 
thorium  salts  emit  a  rays,  the  a  rays  probably  coming  from  the  uranium  and 
thorium  atoms  themselves,  before  they  break  down  into  the  next  radio-active 
product.  If  one  had  a  very  thin  layer  of  a  uranium  or  thorium  salt,  it  would 
be  expected  that  the  range  of  most  of  the  a  particles  would  be  less  if  the  ura- 
nium or  thorium  existed  as  an  aggregate  or  in  the  simple  molecular  condi- 
tion. It  might,  therefore,  be  found  that  the  range  of  the  a  particles  from 
uranyl  nitrate  would  be  related  to  the  wave-length  of  the  uranyl  or  uranous 


56  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

absorption  bands.  Knowing  something  of  the  electromagnetic  forces  neces- 
sary to  alter  the  path  of  the  a  particles,  it  might  be  possible  to  find  some  of 
the  properties  of  the  fields  of  force  that  exist  in  the  neighborhood  of  the  ura- 
nium and  thorium  atoms,  and  the  correlated  effects  upon  the  frequency  of 
the  absorption  bands.  Similar  effects  might  be  obtained  in  the  case  of  the 
/3  and  7  rays.  The  particles  of  the  active  deposits  might  also  be  used  as 
nuclei  about  which  aggregates  would  be  formed. 

Another  possible  method  of  studying  aggregates  is  by  the  phosphores- 
cence produced  by  a  and  )3  rays.  The  effect  of  changes  in  temperature  could 
also  be  taken  up  in  this  connection.  Several  workers  have  concluded  that 
the  phosphorescence  produced  by  the  bombardment  of  certain  kinds  of  screens 
by  a  rays  is  not  due  to  the  breaking  up  of  crystals  along  lines  or  planes  of 
cleavage,  but  that  it  is  due  to  the  breaking  up  of  aggregates  that  are  of 
approximately  molecular  dimensions;  and  that  unless  such  aggregates  are  pres- 
ent, no  phosphorescence  is  produced.  For  example,  pure  zinc  sulphide  is  not 
phosphorescent,  but  when  there  are  impurities  present  phosphorescent  scin- 
tillations can  be  produced.  It  is  probable  that  in  most  phosphorescent  screens 
there  are  a  large  number  of  active  centers  present.  When  the  centers  on  the 
surface  are  destroyed,  those  farther  in  the  screen  will  become  sources  of  scin- 
tillations. When  the  screen  is  new,  each  bombarding  a  particle  probably 
excites  a  considerable  number  of  centers.  As  the  bombardment  is  continued 
the  number  of  centers  excited  by  each  a  particle  decreases,  although  each  par- 
ticle will  excite  one  or  more  centers,  so  that  only  the  intensity  and  not  the 
number  of  scintillations  is  decreased.  The  calculated  diameters  of  the  active 
centers  of  zinc  sulphide  and  willemite  are  of  molecular  magnitude,  whereas, 
in  the  case  of  barium  platinocyanide,  the  diameter  is  about  a  hundred  times 
this  size.  Marsden1  has  found  that  the  number  of  scintillations  is  slightly 
less  at  100°  than  at  15°. 

It  would  be  interesting  to  prepare  salts  so  that  various  solvates  and  aggre- 
gates would  be  found,  and  then  study  the  scintillations  produced  by  them. 
The  above  suggestions  are  made  since  they  are  along  somewhat  different 
lines  than  those  usually  followed  in  the  study  of  solutions. 

NEODYMIUM  CHLORIDE  IN  ETHYL  ACETATE  AND  ANTHRACENE. 

It  was  supposed  by  the  older  writers  on  the  absorption  spectra  of  solu- 
tions, that  if  two  colored  salts  were  dissolved  in  the  same  solution  the  fre- 
quencies of  the  absorbing  centers  of  the  one  salt  would  be  modified  by  the 
presence  of  the  other  salt,  if  the  frequencies  of  the  absorbing  centers  of  the 
latter  were  almost  the  same  as  those  of  the  former.  Several  attempts  have 
been  made  to  test  this  theory  by  experiment,  but  thus  far  no  case  is  known 
where  such  an  effect  is  shown,  at  least  by  the  inorganic  salts. 

According  to  our  theory  of  aggregates  we  would  hardly  expect  any  two 
absorbing  centers  to  have  any  mutual  effects  on  each  other,  unless  both  centers 
were  part  of  the  same  aggregate.  It  is,  however,  quite  difficult  to  find  any 
solution  containing  such  aggregates;  indeed,  it  is  doubtful  if  there  are  any 
that  contain  absorbing  centers  that  have  bands  in  the  same  region  of  the 


1  Proc.  Roy.  Soc.,  84,  A,  548  (1910). 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS.  57 

visible  part  of  the  spectrum.  This  line  of  work  seems  to  be  much  more  promis- 
ing in  the  infra-red. 

It  is  known  that,  in  the  ultra-violet,  anthracene  and  the  neodymium 
salts  have  absorption  bands  that  are  near  together.  It  was,  therefore,  hoped 
that  a  neodymium  salt  dissolved  in  anthracene  would  form  aggregates  con- 
taining both  of  these  compounds,  and  that  the  resultant  absorption  spec- 
trum would  not  be  simply  the  superposition  of  the  two  separate  absorption 
spectra  of  the  given  neodymium  salt  and  anthracene.  Unfortunately,  the 
neodymium  salts  that  were  tried  were  not  soluble  in  anthracene,  and  it  seems, 
therefore,  unlikely  that  we  obtained  aggregates  containing  both  salts.  Never- 
theless, some  spectrograms  were  taken  with  this  idea  in  mind.  Neodymium 
nitrate  and  anthracene  are  both  soluble  in  ethyl  acetate,  and  several  solutions 
containing  these  three  substances  were  prepared.  It  was  found  that  only  very 
dilute  solutions  of  anthracene  allowed  the  ultra-violet  part  of  the  spectrum 
to  be  transmitted,  and  no  good  photograph  was  obtained  that  showed  the 
anthracene  and  neodymium  nitrate  ultra-violet  bands  on  the  spectrogram. 
It  would  seem  very  doubtful  that  any  effect  would  be  obtained,  because  of 
the  improbability  of  anthracene  and  neodymium  nitrate  being  contained  in 
the  same  aggregate. 

A  and  B,  plate  11,  give  the  absorption  spectrum  of  neodymium  nitrate 
and  anthracene  dissolved  in  ethyl  acetate.  In  these  spectrograms  the  ultra- 
violet absorption  is  so  great  that  none  of  the  anthracene  bands  are  shown. 
A  and  B,  plate  12,  represent  neodymium  nitrate  and  anthracene  in  ethyl 
acetate.  The  lower  strip  of  B  shows  several  of  the  ultra-violet  bands  of 
anthracene,  but  does  not  show  any  of  the  neodymium  ultra-violet  bands.  The 
upper  strip  of  B  shows  the  neodymium  bands  quite  clearly,  and  also  the  very 
great  general  ultra-violet  absorption.  It  is  hoped  that  this  effect  can  be 
satisfactorily  tested  with  reference  to  the  theory  of  aggregates,  especially  in 
the  infra-red. 

THE  URANYL  AND  URANOUS  BANDS. 

The  uranyl  bands  are  usually  ten  or  twelve  in  number  and,  starting  at 
about  X  5000,  have  been  designated  by  the  letters  a,  b,  c,  etc.,  and  form  a  series, 
the  head  band  being  the  n  band.  The  uranous  bands  appear  throughout  the 
spectrum  and  do  not  form  any  series.  The  uranous  bands  are  characteristic 
of  the  uranous  salts,  and  spectrograms  of  the  absorption  spectra  of  a  uranous 
salt  gradually  oxidized  into  a  uranyl  salt  by  the  addition  of  hydrogen  peroxide 
show  the  complete  independence  of  the  two  spectra. 

A  problem  of  considerable  interest,  and  one  that  seems  capable  of  solu- 
tion, is  the  complete  correlation  of  the  a,  6,  c,  ...  bands  for  the  various 
uranyl  salts  in  each  solvent.  For  most  solvents  the  uranyl  bands  of  the  dif- 
erent  uranyl  salts  are  very  much  alike.  In  aqueous  solutions  the  differences 
are  very  marked,  but  by  taking  spectrophotographs  of  the  transformation  of 
one  salt  into  another  salt1  Jones  and  Strong  have  succeeded  in  obtaining  many 
relationships  of  this  kind.  By  extending  the  work  to  low  temperatures,  and 
to  the  partly  overlapping  phosphorescent  band  spectra,  it  ought  to  be  possible 
to  connect  continuously  the  various  changes  that  these  bands  undergo. 

1  Publication  130,  Carnegie  Institution  of  Washington. 


58 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


OXIDIZATION  OF  URANOUS  TO  URANYL  SALTS  IN   SOLUTION. 

Some  spectrophotographs  have  been  made  of  the  formation  of  a  uranous 
salt  from  a  uranyl  salt  by  the  nascent  hydrogen  reduction  method.  These 
spectrograms  are  somewhat  unsatisfactory,  since  there  is  a  considerable 
amount  of  gas,  opaque  residues,  etc.,  formed,  and  the  reduction  takes  a  con- 
siderable length  of  time.  It  is  hoped  in  the  future  that  this  reduction  may  be 
produced  by  the  action  of  occluded  hydrogen  (for  example  in  palladium)  that 
will  be  liberated  on  being  heated,  or  by  some  other  method  that  will  not 
require  the  addition  of  other  acids  or  salts. 

The  reverse  process  of  the  oxidization  of  uranous  salts  in  solution  is  a 
very  satisfactory  one,  and  the  spectrograms  can  be  photographed  very  well 
indeed.  This  method  simply  consists  in  the  addition  of  a  small  amount  of 
hydrogen  peroxide  to  the  uranous  solution.  The  spectrophotography  of 
these  reactions,  as  already  mentioned,  has  furnished  an  admirable  method 
by  means  of  which  the  uranyl  and  uranous  bands  can  be  completely  separated. 
Several  oxidizing  agents  have  been  added  to  aqueous  and  alcohol  solutions 
of  uranous  salts  that  showed  both  the  water  and  alcohol  bands,  in  order  to 
see  whether  there  is  any  selective  oxidation. 

OXIDIZATION  OF  URANOUS  CHLORIDE  BY  HYDROGEN  PEROXIDE. 

The  first  solution  of  uranous  chloride  to  be  oxidized,  in  order  to  compare 
the  effect  of  the  presence  of  acid  and  of  other  salts,  was  that  of  the  very 
intensely  colored  solution  of  uranous  chloride  formed  by  reducing  an  ether 
solution  of  uranyl  chloride.  To  one  part  of  this  solution  were  added  four  parts 
of  water,  and  this  required  for  oxidization  about  a  one-fourth  part  of  a  solu- 
tion of  hydrogen  peroxide.  A  cloudy  and  semi-transparent  precipitate  was 
formed  during  oxidization.  When  one  part  of  the  ether  solution  of  uranous 
chloride  was  added  to  six  parts  of  concentrated  hydrochloric  acid,  the  result- 
ant liquid  contained  a  cloudy  precipitate.  The  addition  of  a  few  drops  of 
hydrogen  peroxide  clarified  the  solution,  but  it  required  over  two  parts  of 
hydrogen  peroxide  before  the  uranous  chloride  was  completely  oxidized. 
Following  are  the  tabulated  results  of  these  experiments: 


Parts 
uranous 
chloride 
solution. 

Parts  of  solvent  added. 

Parts 
hydrogen 
peroxide  in 
water 
necessary  for 
oxidization. 

o 

4  0  water                             

0  6 

.0 
.0 
.0 
.0 
.0 

o 

6.0  hydrochloric  acid.     Soluble  
12  .  0  A1C13  in  water.   Small  precipitate  .... 
6  .  0  Cone.  HNO3.    Only  partly  oxidized  .  . 
10.0  acetic  acid.    Precipitate  formed  
12.0  ethyl  alcohol  
12  0  glycerol 

2.0 
0.7 
3.0 
0.7 
0.5 
0  7 

.0 
.0 

12  .  0  methyl  alcohol.    Precipitate  formed.  .  . 
12.0  Ca(NO3)2  in  2H2O  and  3CH4O.    Pre- 
cipitate 

0.6 

0  4 

o 

90  0  ethyl  alcohol 

0  6 

.0 

12.0  water,  4.0  NaClO4  in  water,  and  HC1. 

1.0 

A  solution  of  uranous  chloride  in  water  was  prepared  in  the  usual  manner, 
and  made  strongly  acid  by  the  addition  of  hydrochloric  acid,  in  order  to 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS.  59 

increase  the  stability  of  the  solution.  Solutions  of  uranous  salts  sometimes 
form  precipitates  on  standing.  Uranous  chloride  was  dissolved  in  the  follow- 
ing solvents,  and  mixed  with  the  following  compounds: 


Parts 
uranous 
chloride 
solution. 

Parts  of  solvent  added. 

Parts  of  hydrogen  peroxide 
necessary  for  oxidization. 

1   0 

10  0  water 

0  2 

1.0 

10.0  ethyl  alcohol  

0.2 

1.0 

1  0 

10.0  glycerol  
10  0  hot  water 

0.35 
0  2  precipitated 

1.0 
1.0 
1  0 

10.0  water  M-H^O.,  
10  .  0  acetic  acid  
10  0  acetone 

0.1 
0.2 
0  2  precipitated 

3.0 

1.0 
1.0 
1.0 
1.0 
1.0 
1.0 
3  0 

10  .  0  nitric  acid  
10.0  calcium  nitrate  in  2H2O  +  3CH4O  .  . 
10.0  hydrochloric  acid  
10.0  aluminium  chloride  in  water  
10.0  sodium  perchloride  in  water  
10  .  0  aluminium  chloride  in  hot  water  
7  .  0  hot  hydrochloric  acid  
8  0  hot  nitric  acid 

2.0 
0.2 
2.0 
0.25 
0.2 
0.16 
0.8 
0  0  NO,  formed 

A  spectrogram  was  made  showing  the  effect  of  the  addition  of  hydrogen 
peroxide  to  a  solution  of  about  0.75  normal  concentration  of  an  aqueous  solu- 
tion of  uranous  chloride.  The  uranous  chloride  solution  did  not  show  any 
uranyl  bands  at  all,  and  even  when  the  uranous  bands  appeared  very  strongly 
there  was  very  little  absorption  in  the  region  from  X  3500  to  X  4200.  The  edges 
of  the  uranous  bands  were  well  denned,  there  being  four  very  strong  bands 
extending  between  the  following  limits:  X  4250  to  X  4400,  X  4700  to  about 
X  5080,  X  5400  to  X  5600,  and  X  6100  to  X  6800.  The  transmission  between 
these  bands  was  quite  strong  and  appeared  to  be  uniformly  distributed. 

The  addition  of  hydrogen  peroxide  caused  the  uranous  bands  to  decrease 
in  intensity.  As  far  as  the  quite  sharp  uranous  bands  are  concerned  it  seems 
that  the  individuality  of  these  bands  decrease  at  about  the  same  rate;  but 
the  X  4340  band  is  replaced  by  the  blue-violet  uranyl  band,  and  the  X  5500 
band  is  also  apparently  replaced  by  wide  general  absorption  in  this  region, 
extending  500  or  600  Angstrom  units.  On  the  other  hand,  the  transmission 
seems  to  be  pretty  complete  in  the  red  and,  with  the  exception  of  the  very 
weak  uranyl  bands,  in  the  region  X  4500. 

A,  plate  44,  represents  the  effect  of  the  addition  of  hydrogen  peroxide  to 
a  solution  of  uranous  chloride  in  water,  acetone,  and  hydrochloric  acid.  The 
solution  did  not  contain  the  right  proportion  of  the  solvents  to  show  the  fine 
structure  of  the  uranous  and  uranyl  bands  brought  out  by  some  acid  acetone 
solutions.  The  spectrogram  shows  very  clearly  the  various  uranous  bands, 
and  how  they  are  replaced  by  the  uranyl  bands  as  hydrogen  peroxide  is  added. 

The  band  that  appears  at  about  X  4970,  and  is  quite  strong  on  several 
of  the  strips,  is  a  uranous  band,  and  disappears  when  sufficient  hydrogen 
peroxide  is  added.  In  the  upper  strip,  which  represents  the  absorption  of  the 
uranyl  salt,  there  is  a  wide,  very  diffuse  and  weak  region  of  absorption,  running 
from  about  X  5000  to  X  5100. 


60  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

In  addition  to  the  ordinary  uranous  and  uranyl  bands,  there  is  a  weak 
band  about  15  Angstrom  units  wide  at  about  X  5080.  This  band  appears 
best  in  the  central  strips,  and  can  hardly  be  detected  at  all  in  the  lowest  and 
highest  strips.  It  is,  therefore,  difficult  to  say  whether  it  is  a  uranyl  or  a 
uranous  band.  In  fact  it  may  not  be  due  to  either  of  the  two  uranium  salts. 
The  band  is  very  similar  to  the  one  described  under  the  oxidization  of  uranous 
chloride  in  hydrochloric  acid,  only  with  the  exception  that  the  bands  have  very 
different  wave-lengths. 

OXIDIZATION    OF    URANOUS    CHLORIDE    IN    HYDROCHLORIC   ACID 
BY    HYDROGEN    PEROXIDE. 

It  seems  that  the  acid  uranous  aggregates  are  in  general  more  stable 
than  the  neutral  aggregates.  Hydrogen  peroxide  oxidizes  the  strongest  acid 
solutions.  A  spectrogram  was,  however,  made  of  a  neutral  uranous  chloride 
solution,  to  which  a  large  amount  of  concentrated  hydrochloric  acid  had  been 
added,  and  to  which  increasing  amounts  of  hydrogen  peroxide  were  added. 
The  addition  of  the  hydrochloric  acid  caused  the  uranous  chloride  bands  to 
be  shifted  about  100  Angstrom  units  towards  the  red.  In  other  respects  the 
bands  were  not  greatly  changed,  with  the  exception  of  the  bands  in  the  red. 

The  uranous  bands,  on  the  addition  of  hydrogen  peroxide,  gradually 
decreased  in  intensity  without  having  their  wave-length  changed.  At  the 
same  time  the  uranyl  bands  appeared  and,  as  is  the  case  for  strongly  acid 
solutions,  the  uranyl  bands  appeared  quite  sharp  and  intense. 

It  may  be  supposed  that  in  the  case  of  the  existence  of  acid  aggregates 
it  would  require  a  longer  time  for  the  oxidization  to  take  place  than  in  the  case 
where  only  neutral  aggregates  are  present.  It  would  be  interesting  to  know 
what  the  reaction  velocities  of  these  oxidization  reactions  are  for  the  various 
kinds  of  aggregates. 

It  is  a  difficult  matter  to  preserve  uranous  nitrate  in  the  uranous  condi- 
tion. When  uranyl  nitrate  is  mixed  with  nitric  acid  and  zinc  is  added,  some 
uranous  nitrate  is  formed,  but  it  is  soon  re-transformed  into  the  uranyl  con- 
dition. This  would  indicate  that  uranous  nitrate  in  water  containing  nitric 
acid  is  unstable  and  is  quickly  oxidized.  On  the  other  hand,  uranous  chlo- 
ride can  be  mixed  with  concentrated  nitric  acid  and  the  uranous  absorption 
spectrum  will  be  found  to  be  entirely  different  from  that  of  uranous  chloride. 
In  this  case  the  uranous  salt  will  remain  as  such  for  at  least  a  day  or  two 
when  kept  at  room  temperatures.  This  may  be  explained  by  supposing  that 
the  nitric  acid  aggregate  of  uranous  nitrate  is  much  more  stable  than  the 
salt  itself. 

According  to  the  law  of  mass  action,  if  a  nitrate  is  mixed  with  uranous 
chloride,  some  uranous  nitrate  ought  to  be  formed.  To  test  the  stability 
of  uranous  nitrate,  uranous  chloride  was  dissolved  in  a  solution  of  calcium 
nitrate  in  water  and  methyl  alcohol.  Under  these  conditions  both  "water" 
and  "alcohol"  bands  appeared.  This  solution  did  not  oxidize,  but  a  black 
precipitate  was  formed.  This  experiment  could  also  be  explained  by  suppos- 
ing that  the  uranous  nitrate  in  this  solution  existed  in  the  condition  of  some 
kind  of  an  aggregate.  The  precipitate  formed  appeared  to  be  similar  to  that 
which  is  formed  on  heating  a  neutral  uranous  salt  to  the  boiling-point. 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS.  61 

Uranyl  chloride,  hydrochloric  acid,  and  potassium  nitrate  were  mixed  in 
water  and  methyl  alcohol,  and  zinc  was  added.  The  reduction  took  place  easily 
and  the  resulting  uranous  salt  remained  stable.  It  is  probable  that  in  this 
case,  also,  more  stable  aggregates  than  neutral  uranous  nitrate  were  formed. 
As  a  reciprocal  reaction,  uranyl  nitrate,  aluminium  chloride,  and  hydrochloric 
acid  (in  small  quantity)  were  dissolved  in  water  and  zinc  added.  A  stable 
solution  of  a  uranous  salt,  probably  largely  chloride,  was  formed.  In  this 
case  very  little  uranyl  nitrate  existed  in  the  solution  after  the  aluminium 
chloride  and  hydrochloric  acid  were  added.  These  three  experiments  would 
then  indicate  that  there  is  probably  but  little  oxidization  of  uranous  chloride 
to  the  uranyl  salt  under  these  conditions. 

THE    OXIDIZATION    OF    URANOUS   SULPHATE. 

The  preparation  of  concentrated  aqueous  solutions  of  uranous  chloride 
and  uranous  bromide  is  not  difficult,  using  the  method  of  reduction  of  the 
corresponding  uranyl  salt  with  nascent  hydrogen.  A  concentrated  aqueous 
solution  of  uranous  sulphate  can  be  obtained  in  a  similar  manner,  but  on 
standing  almost  all  of  the  uranium  is  precipitated.  The  presence  of  sulphuric 
acid,  however,  enabled  us  to  prepare  a  far  more  concentrated  solution  of 
uranous  sulphate,  and  this  was  quite  stable. 

A  solution  of  uranous  sulphate  was  prepared  by  reducing  uranyl  sulphate 
with  nascent  hydrogen.  The  precipitate  formed  was  partly  dissolved  in  water. 
The  aqueous  solution  of  uranous  sulphate  thus  prepared  was  approximately 
0.1  normal,  and  was  fairly  stable  when  kept  in  ground-glass  stoppered  bottles. 
When  exposed  to  the  air  it  oxidized  slowly  to  the  uranyl  condition.  The 
addition  of  methyl  alcohol,  ethyl  alcohol,  or  acetone  to  the  aqueous  solution 
of  uranyl  sulphate  precipitated  some  of  the  salt. 

A  spectrogram,  B,  plate  35,  shows  the  oxidization  of  an  aqueous  solution 
of  uranous  sulphate  to  uranyl  sulphate,  by  the  addition  of  an  aqueous  solution 
of  hydrogen  peroxide. 

The  original  film  shows  quite  a  large  number  of  the  uranyl  bands.  The 
wave-lengths  of  the  uranyl  bands  seem  somewhat  greater  than  those  of  uranyl 
sulphate  solutions  made  from  the  chemically  pure  salt.  This  is  probably  due 
to  the  presence  of  a  considerable  amount  of  zinc  sulphate.  In  addition  to  the 
regular  uranyl  sulphate  bands  there  is  present  quite  a  fine  and  weak  band  at 
X  5100.  This  band  does  not  seem  to  vary  to  any  considerable  extent  from 
strip  to  strip,  and  it  is  difficult  to  say  whether  it  is  a  uranyl  or  a  uranous  band. 

THE   OXIDIZATION  OF  URANOUS  BROMIDE  BY  HYDROGEN  PEROXIDE. 

An  aqueous  solution  of  uranous  bromide  is  oxidized  by  hydrogen  peroxide 
in  the  same  way  that  uranous  chloride  is  oxidized.  The  absorption  spectra  of 
the  bromide  and  chloride  are  quite  similar  for  the  uranyl  and  the  uranous  salts. 

A  solution  of  uranous  bromide  in  ethyl  alcohol  is  oxidized  by  hydrogen 
peroxide.  In  the  case  photographed  the  alcoholic  solution  had  a  very  great 
ultra-violet,  violet,  and  blue  absorption  after  the  oxidization  had  taken  place. 

B,  plate  44,  represents  the  oxidization  of  a  glycerol  solution  by  the  addition 
of  hydrogen  peroxide.  In  addition  to  a  few  of  the  uranyl  bands,  the  character- 
istic uranous  glycerol  bands  consist  of  a  wide  diffuse  band  atX  4400  and  a  strong 


62  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

and  quite  persistent  band  at  X  4680.  This  is  about  the  most  persistent  band 
in  the  uranous  spectrum,  although  in  the  lower  strip  it  is  only  about  40 
Angstrom  units  in  width ,  while  the  red  band  is  about  ten  times  as  wide.  The 
bands  XX  4400,  5000,  and  5250  are  very  much  alike,  being  about  100  Angstrom 
units  in  width,  very  weak  and  diffuse.  The  band  X  5000  is  apparently  double. 
The  red  band  is  quite  strong,  running  from  X  6050  to  X  6400.  It  is  accompanied 
by  a  very  weak  band  at  X  6600.  This  band  is  extremely  weak,  and  probably 
corresponds  to  the  water  band  in  the  same  region.  The  addition  of  hydrogen 
peroxide  simply  causes  each  one  of  these  bands  to  decrease  in  intensity,  while 
the  uranyl  bands  increase  in  intensity. 

A  POSSIBLE  METHOD  OF  MEASURING  THE  STRENGTHS  OF  ACIDS. 

Several  methods  have  been  employed  for  measuring  the  relative  strengths 
of  acids.  Among  these  are :  The  power  of  acids  to  divide  a  base  between  them, 
as  determined  by  thermo-chemical  and  volume-chemical  methods;  their  power 
to  invert  cane-sugar;  to  saponify  an  ester;  to  convert  acetamide  into  am- 
monium acetate;  their  conductivity,  etc.  All  of  these  methods  measure  the 
relative  concentrations  of  the  hydrogen  ions  in  the  solutions  of  the  various 
acids,  the  degree  of  dissociation  determining,  of  course,  the  relative  strengths 
of  acids.  All  acids  at  infinite  dilution,  or  when  completely  dissociated,  are, 
then,  of  the  same  strength.  In  more  concentrated  solutions  the  strengths 
of  acids  vary  directly  as  their  dissociation.  Our  work  on  absorption  spectra 
has  shown  that  the  positions  of  the  uranyl  and  the  uranous  bands  for  different 
uranium  salts  are  often  quite  different.  We  could  add  just  enough  of  the  acid 
in  question  to  transform  completely  the  original  salt  into  the  salt  of  the  acid 
in  question,  and  then  express  the  concentration  of  the  acids  and  salts  in  gram 
molecules  per  liter,  or  by  any  other  convenient  method. 

Some  spectrograms  of  this  kind  have  been  made  indicating  the  relatively 
great  strength  of  hydrochloric  acid.  As  yet,  however,  the  subject  has  only 
been  touched  upon.  It  is  important  that  an  accurate  quantitative  method  for 
measuring  the  intensity  and  wave-length  of  the  bands  be  first  devised.  There 
will  be  one  obstacle  that  may  cause  some  difficulty  in  this  method,  and  that 
is  the  presence  of  the  acid  (above,  the  acetic  acid)  displaced  from  the  colored 
salt  by  the  addition  of  the  acid  to  be  tested. 

Experiments  of  this  kind  should  be  carried  out  with  various  uranyl, 
uranous,  and  neodymium  salts,  etc.,  in  different  solvents,  to  find  whether  the 
relative  strengths  of  acids  are  the  same  for  the  various  colored  salts,  for  the 
different  solvents,  for  different  concentrations,  for  different  temperatures, 
for  salts  when  in  the  presence  of  colorless  salts,  etc.  Spectrophotography 
of  this  kind  only  includes  a  study  of  the  spectra  as  they  are  changed  from  that 
of  one  neutral  salt  to  that  of  another.  Such  a  method,  however,  could  hardly 
be  made  as  accurate  a  measure  of  the  strength  of  acids  as  the  conductivity 
method,  and  not  nearly  so  general. 

ARE  THE  IONS  FACTORS  IN  THE  ABSORPTION  OF  LIGHT? 
It  is  one  of  the  remarkable  facts  brought  out  in  this  investigation,  that 
ions  as  such  do  not  seem  to  play  any  role  in  the  absorption  of  light.  If  the 
ions  were  the  absorbers  of  light  in  solution,  then  the  absorption  spectrum  of 
a  solution  would  vary  with  the  dilution  of  the  solution,  since  the  dissociation 
of  a  solution  varies  with  the  dilution. 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS. 


63 


There  are  solutions  of  the  different  colored  salts  of  a  certain  metal,  for 
which  the  wave-lengths  of  the  absorption  bands  are  different.  It  will  be 
remembered  in  the  case  of  neodymium  that  the  absorption  spectra  of  the 
acetate,  chloride,  and  nitrate  are  quite  different  from  one  another.  The 
spectra  of  these  salts  should  all  be  the  same,  in  dilute  solution,  if  the  absorp- 
tion of  light  were  due  solely  to  the  ions. 

Jones  and  Guy  are  now  studying  very  dilute  solutions  of  certain  salts, 
to  see  whether  there  is  any  detectable  difference  between  the  spectrograms 
in  very  dilute  and  in  more  concentrated  solutions. 

There  are  not  many  cases  known  where  the  wave-lengths  of  the  absorp- 
tion bands  of  different  salts  of  the  same  metal  in  the  same  solvent  are  very 
different.  Uranyl  nitrate  in  water,  however,  gives  bands  that  are  of  quite 
different  wave-lengths  from  those  given  by  other  uranyl  salts  in  water.  The 
following  will  illustrate  this  point : 


a 

b 

c 

d 

/ 

Uranyl  nitrate  .  . 
Uranyl  sulphate  .  . 

.  .   4870 
..   4900 

4705 
4740 

4550 
4580 

4460 

4310 
4330 

4155 
4200 

While  previous  work  of  Jones  and  Strong1  indicated  that  there  was  little 
or  no  change  in  the  positions  of  the  nitrate  and  sulphate  bands  with  change 
in  concentration,  recent  experiments  made  with  the  concentrations  0.5  and 
0.003  normal  indicate  that  in  the  more  dilute  solutions  the  sulphate  bands 
have  been  slightly  shifted  towards  the  violet,  while  the  nitrate  bands  have 
been  slightly  shifted  towards  the  red.  It  may  be  possible  that,  with  sufficient 
dilution,  the  sulphate  and  nitrate  bands  would  occupy  the  same  position,  as 
would  be  the  case  if  the  ions  were  the  only  absorbers  in  the  solutions;  yet  the 
shifts  are  so  small  with  the  dilution  that  this  seems  improbable. 

Indeed,  it  has  recently  been  shown  by  Jones  and  Guy,  working  in  very 
dilute  solutions  and  with  a  depth  of  layer  of  250  cm.,  that  the  uranyl  nitrate 
bands  are  only  very  slightly  shifted  towards  the  red,  and  the  uranyl  sulphate 
bands  are  only  very  slightly  shifted  towards  the  violet.  The  evidence  is  there- 
fore convincing  that  the  presence  of  the  N03  and  the  SO4  groups  influ- 
ences the  periods  of  the  absorbing  centers  in  the  uranyl  atoms  or  groups. 
Another  good  example  that  can  be  tested  in  a  similar  way  is  that  of  uranyl 
chloride  and  uranyl  nitrate  in  acetone.  These  uranyl  bands  are  quite  strong, 
and  the  difference  in  the  wave-lengths  of  corresponding  bands  is  at  least  from 
50  to  60  Angstrom  units. 


Uranyl  nitrate  in  acetone  
Uranyl  chloride  in  acetone  

4840 
{S}doub,e 

4665 

Jig}*— 

4515 
4610 

Such  facts  as  the  above  can  be  readily  explained  in  terms  of  the  theory 
of  aggregates.  A  uranyl  nitrate  aggregate  loses  an  NOa  group,  and  becomes 
an  ionized  aggregate  or  complex  ion.  The  loss  of  the  N03  group  causes  a 
decrease  in  the  hypsochromous  effect,  but  this  would  be  smaller  if  the  aggre- 
gate were  large.  There  would  be  a  similar  result  in  the  case  of  the  uranyl 

1  Proc.  Amer.  Phil.  Soc.,  48, 192  (1909). 


64  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

sulphate  aggregates.    It  is,  however,  surprising  that  these  aggregates,  if  they 
exist,  are  not  broken  up  when  the  solution  becomes  very  dilute. 

It  is  important  that  acid  aggregates  should  be  studied  in  the  same  way. 
It  is  possible  that  these  would  break  up  more  easily  with  increase  in  dilution 
than  the  neutral  aggregates  apparently  do. 

THE   OXIDIZATION    OF    URANOUS    SALTS   BY    NITRIC   ACID. 

On  account  of  the  very  great  instability  of  uranous  nitrate,  it  was  ex- 
pected that  the  addition  of  concentrated  nitric  acid  to  aqueous  solutions  of 
the  other  uranous  salts  would  cause  their  rapid  oxidization.  In  the  case  of 
uranous  bromide,  bromine  was  given  off.  In  general,  the  addition  of  nitric 
acid  to  an  aqueous  solution  of  uranous  chloride  causes  the  oxidization  of  that 
salt,  but  if  a  large  amount  of  nitric  acid  is  added,  the  solution  changes 
from  a  very  deep  green  to  a  light  greenish-yellow,  and  the  absorption  spec- 
trum shows  that  there  is  still  a  very  considerable  amount  of  uranous  salt  in 
the  solution;  and  the  bands  are  quite  different  from  those  of  neutral  uranous 
chloride.  This  uranous  solution  will  remain  for  days,  and  seems  to  be  quite 
stable. 

A,  plate  45,  represents  the  absorption  of  a  solution  of  uranous  bromide 
in  water  and  methyl  alcohol  to  which  dilute  nitric  acid  is  added  in  increasing 
amounts.  The  addition  of  the  nitric  acid  caused  a  slight  increase  in  the  trans- 
mission in  the  ultra-violet,  but  this  was  quite  small.  The  uranyl  bands  appear, 
but  are  very  weak.  In  strip  1  there  is  a  band  running  from  X  4200  to  X  4400. 
This  is  probably  due  to  a  water  and  alcohol  band,  the  alcohol  band  being  on 
the  red  side.  Apparently  the  alcohol  band  disappears,  since  the  band  nar- 
rows rapidly  on  its  red  side,  and  then  decreases  slowly  in  intensity.  The  alco- 
hol band  at  X  4650  has  practically  disappeared  in  the  third  strip.  In  strip  1 
there  is  a  weak,  very  diffuse  band  at  X  4800,  and  a  strong  band  at  about  X  4950. 
As  nitric  acid  is  added  these  bands  are  replaced  by  a  wide  and  strong  region 
of  absorption,  running  from  X  4600  to  X  5000.  The  band  X  5200  disappears. 
The  band  X  5500  is  shifted  about  150  Angstrom  units  towards  the  violet.  The 
alcohol  band  running  from  about  X  6000  to  X  6300  narrows  rapidly  on  its  short 
wave-length  edge,  disappears,  and  is  replaced  by  a  weak,  diffuse  band  at  about 
X  6100.  The  red  water  bands  increase  and  then  gradually  decrease  in  inten- 
sity. When  this  decrease  begins,  the  long  wave-length  band  is  much  the 
stronger  of  the  two  and  indicates  that  the  uranous  bromide  alcoholate  and 
the  uranous  bromide  hydrate  have  both  been  changed  to  some  uranous  nitrate 
hydrate,  and  that  this  compound  is  then  oxidized  to  the  uranyl  salt. 

The  addition  of  nitric  acid  to  the  aqueous  solution  of  uranous  sulphate 
previously  described  produces  a  slow  oxidization  of  the  uranous  into  the  ura- 
nyl salt.  This  oxidization  requires  several  minutes  and  would  be  a  very  good 
reaction  with  which  to  study  reaction  velocity,  the  intensity  of  the  absorp- 
tion bands  being  determined  by  a  radiomicrometric  method.  B,  plate  46,  is 
a  spectrograph  of  the  oxidization  produced  by  adding  nitric  acid  to  an  aqueous 
solution  of  uranous  sulphate.  Strip  5  is  the  absorption  of  the  same  solution 
as  that  shown  by  strip  4,  the  only  difference  being  that  the  solution  had 
been  allowed  to  stand  for  several  minutes. 

In  the  solution  of  uranous  sulphate  oxidized  by  nitric  acid,  the  uranyl 
bands  are  shifted  slightly  towards  the  violet,  compared  with  the  uranyl  bands 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS.  65 

of  the  uranous  sulphate  solution  oxidized  by  hydrogen  peroxide,  showing  that 
probably  some  uranyl  aggregate  is  formed  that  contains  some  NO3  groups. 

The  addition  of  the  first  amount  of  nitric  acid  causes  the  transmission 
in  the  ultra-violet  to  be  increased  very  greatly,  with  the  appearance  of  a  large 
number  of  the  uranyl  bands.  In  the  red  the  wide  uranous  sulphate  band  is 
decreased  in  intensity.  Strips  2  and  3  show  the  narrow  red  sulphate  water 
band,  but  in  strip  4  this  band  has  completely  disappeared  and  is  replaced 
by  a  single  weak  band  300  Angstrom  units  wide. 

B,  plate  45,  represents  the  change  in  the  absorption  spectrum  of  a  solu- 
tion of  uranous  chloride  in  methyl  alcohol  and  acetone,  to  which  nitric  acid 
is  added.  This  spectrogram  shows  the  rapid  disappearance  of  the  alcohol 
bands.  The  various  uranous  bands  seem  to  be  replaced  by  the  bands  of 
some  hydrate  of  a  uranous  nitrate  aggregate,  and  this  aggregate  is  then  grad- 
ually oxidized.  The  ultra-violet  transmission  increases  until  the  last  strip, 
which  shows  a  very  great  increase  in  the  ultra-violet  absorption.  The  last 
strip  still  shows  the  presence  of  a  considerable  amount  of  uranous  salt,  and 
the  absorption  bands  are  entirely  new. 

A,  plate  37,  represents  the  absorption  spectrum  of  uranous  chloride  as  it 
is  gradually  changed  into  uranous  nitrate  by  the  addition  of  nitric  acid.  B, 
plate  37,  represents  the  corresponding  changes  in  the  absorption  spectra  that 
take  place,  when  to  a  solution  of  uranous  chloride  in  equal  parts  of  water  and 
methyl  alcohol  is  added  nitric  acid  also  dissolved  in  equal  parts  of  water  and 
methyl  alcohol.  The  upper  strip  represents  the  absorption  of  the  resultant 
uranyl  salt  after  oxidization  with  hydrogen  peroxide.  As  the  bands  are  quite 
wide  and  strong  most  of  the  changes  can  be  seen  on  the  plate  itself.  It  will  be 
seen  that  the  absorption  spectrum  of  the  nitric  acid  solution  of  uranous  chlo- 
ride is  very  different  from  that  of  the  neutral  chloride.  This  spectrogram  also 
seems  to  indicate  that  there  is  not  a  gradual  shifting  of  the  chloride  bands 
into  the  nitrate  bands,  but  in  the  case  of  the  X  6300  chloride  band  there  is  a 
decrease  in  intensity  without  being  shifted;  and  this  is  replaced  by  the  uranous 
nitrate  band  at  about  X  6100.  B  shows  that  the  addition  of  nitric  acid  results 
in  a  rapid  and  almost  complete  disappearance  of  the  alcohol  bands,  while  the 
uranous  nitrate  water  bands  increase  in  intensity. 

URANOUS   ACETATE   AND    THE    EFFECT   OF    THE   ADDITION    OF 
NITRIC   ACID. 

The  reduction  of  uranyl  acetate  to  the  uranous  salt  is  not  complete,  and 
a  precipitate  was  formed,  so  that  the  resultant  solution  here  used  was  quite 
dilute.  A  spectrogram  (B,  plate  36)  was  made  of  this  solution,  and  the  first 
four  strips  represent  the  absorption  of  layers  of  different  thicknesses,  for  the 
last  layer  this  being  about  20  cm.  To  this  solution  were  added  10,  20,  and  40 
drops  of  concentrated  nitric  acid,  the  absorption  being  represented  by  strips 
6,  7,  8.  The  first  five  strips  represent  quite  well  the  absorption  of  uranous 
acetate,  and  they  also  show  very  clearly  the  uranyl  acetate  bands.  The 
addition  of  nitric  acid  causes  a  great  increase  in  the  general  transmission 
throughout  the  spectrum,  and  a  very  rapid  decrease  in  the  intensity  of  the 
uranous  bands.  The  resultant  uranous  bands  are,  of  course,  those  of  uranous 
nitrate.  This  spectrogram  shows  that  uranous  acetate  is  quickly  oxidized 
in  the  presence  of  nitric  acid,  whereas  this  is  not  the  case  with  uranous  chloride. 


66 


THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 


THE  SELECTIVE  ACTION   OF   CHEMICAL  REAGENTS   ON   SOLVATES. 

After  photographing  the  effect  of  oxidizing  the  uranous  salts  to  the  uranyl 
condition  by  the  addition  of  hydrogen  peroxide,  it  was  natural  to  study  what 
effect  the  addition  of  other  oxidizating  agents  would  have  upon  the  various 
solvate  bands.  It  will  be  remembered  that  the  addition  of  hydrogen  peroxide 
caused  the  complete  oxidization  of  the  various  solvates  in  the  solution.  It  was 
found  that  the  action  of  the  other  oxidizing  agents  used  was,  in  general,  of  a 
more  or  less  selective  nature. 

A,  plate  47,  represents  the  absorption  of  a  solution  of  uranous  bromide 
in  3.5  parts  water  and  6  parts  methyl  alcohol,  to  which  was  added  calcium 
nitrate  in  methyl  alcohol,  1.2  normal. 


Uranoua  bro- 
mide (amount 
constant). 

Drops  of  cal- 
cium nitrate 
in  methyl 
alcohol. 

Percentage 
water  in 
solution. 

Strip  1  

0                         37 

Strip  2  

10                         33 

Strip  3  

20 

28 

Strip  4  40                     21 

Strip  5  

80                     14 

The  addition  of  calcium  nitrate  causes  a  very  great  increase  in  the  amount 
of  the  general  absorption  of  the  short  wave-lengths.  This  is  to  be  especially 
noticed  in  the  last  addition  of  the  calcium  nitrate.  The  most  important  thing 
to  be  seen  from  this  spectrogram  is  the  rapid  and  almost  total  disappearance 
of  the  water  bands.  The  intensity  of  the  alcohol  bands  changes  very  little, 
if  any,  and  it  seems  quite  improbable  that  the  uranous  hydrate  could  have 
been  converted  into  uranous  alcoholate  without  the  alcohol  bands  increasing 
very  much  in  intensity.  The  natural  conclusion  is  that  the  uranous  hydrate 
has  been  oxidized  to  the  uranyl  condition  by  the  calcium  nitrate.  The  original 
film  shows  that  in  the  third  strip  the  two  red  uranous  water  bands  have  almost 
the  same  intensity.  This  may  mean  that  the  uranous  bromide  has  been 
changed  to  some  other  salt. 

B,  plate  47,  represents  the  absorption  of  a  solution  of  uranous  bromide  in 
2  parts  of  water  and  3  parts  of  methyl  alcohol,  the  resultant  solution  being 
about  0.12  normal.  To  this  were  added  small  amounts  of  a  solution  of  sodium 
perchlorate  in  methyl  alcohol.  It  will  be  seen  that  the  water  bands  decrease 
in  intensity  as  the  sodium  perchlorate  is  added,  and  that  the  longest  wave- 
length water  band  becomes  more  diffuse.  The  reason  why  the  fifth  strip  is 
vacant  is  on  account  of  the  formation  of  a  precipitate.  The  precipitate  was 
not  analyzed,  but  the  spectrogram  shows  that  the  uranous  hydrate  has  almost 
entirely  disappeared  from  the  solution,  while  there  is  still  present  quite  a 
considerable  amount  of  uranous  alcoholate.  This  spectrogram  is,  therefore, 
a  good  example  of  a  case  of  selective  precipitation  of  solvates.  B,  like  A, 
plate  47,  indicates  that  there  is  a  change  in  the  constitution  of  the  uranous 
hydrate  before  it  was  precipitated. 

A,  plate  46,  represents  the  effect  of  the  addition  of  potassium  nitrate  and 
calcium  nitrate  to  a  solution  of  uranous  bromide.  In  strip  1  we  have  the 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS.  67 

absorption  due  to  a  solution  of  uranous  bromide  in  3.5  parts  water  and  6  parts 
methyl  alcohol.  To  this  is  added  a  solution  of  potassium  nitrate  in  2  parts 
water  and  3  parts  methyl  alcohol,  which  results  in  a  precipitate.  The  precipi- 
tate was  filtered  off  and  the  resultant  solution  gives  the  absorption  as  repre- 
sented in  strips  2  and  3.  It  will  be  seen  that  only  the  uranous  hydrate  has 
been  precipitated.  Strip  4  represents  another  solution  of  uranous  bromide  in 
3.5  parts  of  water  and  6  parts  of  methyl  alcohol,  and  to  this  solution  is  added 
calcium  nitrate  dissolved  in  2  parts  of  water  and  3  parts  of  methyl  alcohol. 
The  effect  of  the  addition  of  this  calcium  nitrate  is  to  cause  the  almost  com- 
plete disappearance  of  the  water  bands,  while  the  intensity  of  the  alcohol 
bands  remains  practically  the  same.  In  the  fifth  strip  it  will  be  seen  that  the 
long  wave-length  water  band  is  nearly  150  Angstrom  units  in  width,  and  is 
very  much  wider  than  the  other  red  water  band.  This  spectrogram  furnishes 
striking  evidence  in  support  of  the  view  of  the  selective  oxidization  of  the 
uranous  hydrate  in  this  solution. 

A,  plate  42,  represents  the  absorption  of  uranous  bromide  in  water  and 
methyl  alcohol  to  which  an  aqueous  solution  of  calcium  nitrate  is  added.    The 
spectrogram  shows  the  decrease  in  the  intensity  of  the  alcohol  bands.    This 
is  most  likely  due  to  the  increase  in  the  percentage  of  water  present  in  the 
solution.    The  second  strip  shows  the  very  quick  change  in  the  relative  inten- 
sity of  the  two  red  uranous  water  bands.    This  effect  seems  to  be  a  general 
one  for  the  addition  of  calcium  nitrate  to  solutions  of  uranous  chloride,  bro- 
mide, or  sulphate.    The  spectrogram  does  not  seem  to  indicate  that  any  of 
the  uranous  salt  has  been  oxidized. 

B,  plate  41,  shows  that  when  hydrogen  peroxide  is  dissolved  in  the  same 
proportion  of  water  and  methyl  alcohol  as  the  uranous  bromide,  the  alcohol 
and  water  bands  both  disappear  at  the  same  rate,  indicating  that  hydrogen 
peroxide  has  no  selective  action  on  these  two  solvates. 

The  solution  of  uranous  chloride  used  was  acidulated  with  hydrochloric 
acid,  and  when  mixed  with  an  equal  volume  of  methyl  alcohol  gave  the  water 
and  methyl  alcohol  bands  of  about  the  same  intensity.  Two  solutions  were 
used:  one  (spectrogram  A,  plate  36)  in  which  the  alcohol  bands  were  much  the 
stronger,  and  the  other  (spectrogram  A,  plate  41)  in  which  the  water  bands 
were  slightly  stronger.  Calcium  nitrate  in  2  parts  of  water  and  3  parts 
alcohol  was  added,  the  amounts  being  10,  20,  40,  and  about  120  drops.  The 
last  strip  of  A,  plate  41,  represents  the  result  of  the  addition  of  hydrogen 
peroxide.  Spectrogram  A,  plate  38,  represents  the  effect  produced  by  add- 
ing sodium  chlorate  dissolved  in  equal  parts  of  water  and  alcohol.  In  this 
case  no  oxidization  resulted.  A,  plate  36,  shows  very  little  change  in  either 
the  water  or  the  alcohol  bands.  The  red  water  bands  have  their  relative 
intensity  greatly  changed,  however,  on  the  addition  of  calcium  nitrate.  A, 
plate  41,  shows  this  same  relative  change  in  the  intensity  of  the  two  red  water 
bands.  The  spectrogram  shows  a  very  considerable  increase  in  the  intensity 
of  the  alcohol  bands,  and  a  decrease  in  the  intensity  of  the  water  bands.  A, 
plate  38,  shows  very  little  if  any  change  at  all  in  the  absorption  spectra.  Even 
the  red  water  banols  remain  of  about  the  same  relative  intensity. 

B,  plate  38,  represents  the  absorption  of  one  part  of  uranous  chloride  in 
water  to  which  one  part  of  methyl  alcohol  is  added.  Succeeding  strips,  with 


68  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

the  exception  of  the  last,  represent  the  effect  of  adding  potassium  chlorate  in 
water  and  methyl  alcohol.  The  last  strip  represents  the  effect  of  adding  hydro- 
gen peroxide.  This  spectrogram  shows  the  almost  complete  disappearance  of 
the  water  bands,  while  the  alcohol  bands  remain  of  about  the  same  intensity. 

Plate  43,  A,  represents  the  absorption  of  uranous  chloride  in  one  part  of 
water  and  one  part  of  methyl  alcohol.  Hydrogen  peroxide,  in  equal  volumes 
of  water  and  methyl  alcohol,  was  added  to  this  solution,  three  drops  at  a  time; 
except  to  the  solution  whose  spectrogram  is  shown  in  the  last  strip,  twelve 
drops  of  hydrogen  dioxide  were  added.  The  uranous  alcoholate  and  hydrate 
are  oxidized  to  the  same  extent. 

Plate  43,  B,  represents  the  absorption  due  to  uranous  bromide  0.5  normal 
in  water,  to  which  three  parts  of  methyl  alcohol  were  added.  After  a  time  a 
precipitate  was  formed.  This  was  filtered  off,  and  strip  2  is  the  spectrogram 
of  the  solution.  Successive  strips  represent  the  effect  of  adding  increasing 
amounts  of  potassium  chlorate  in  equal  volumes  of  water  and  methyl  alcohol. 
Very  little,  if  any,  relative  action  manifests  itself. 

A,  plate  27,  represents  the  absorption  of  concentrated  nitric  acid  to  which 
increasing  amounts  of  uranous  chloride  were  added. 

B,  plate  27,  represents  the  absorption  of  the  filtrate  of  a  uranous  bromide 
solution.    A  solution  of  uranous  bromide  of  sufficient  strength  when  mixed 
with  alcohol  to  give  the  water  and  alcohol  bands  of  the  same  intensity  usually 
forms  a  precipitate  if  allowed  to  stand.    Strip  1  shows  the  absorption  of  the 
filtrate  of  such  a  solution,  and  indicates  the  selective  precipitation  of  the 
hydrate.    The  succeeding  strips  represent  the  absorption  of  uranous  bromide 
in  water  and  alcohol,  to  which  is  added  nitric  acid  in  the  same  proportion  of 
water  and  alcohol.     The  last  strip  represents  the  solution  containing  the 
greatest  amount  of  nitric  acid,  to  which  was  added  a  few  drops  of  hydrogen 
peroxide. 

C,  plate  27,  represents  the  absorption  of  uranous  chloride  in  propyl 
alcohol,  to  which  acetone  is  added.    A  gives  what  we  shall  call  the  uranous 
nitrate  spectrum,  although  it  is  probably  quite  different  from  that  of  a  neutral 
aqueous  uranous  nitrate  absorption  spectrum.     B  is  a  good  example  of 
selective  precipitation,  and  of  the  action  of  nitric  acid  in  increasing  the  inten- 
sity of  the  hydrate  bands  at  the  expense  of  the  alcoholate  bands.    C  shows 
how  the  addition  of  acetone  causes  the  almost  complete  disappearance  of  the 
uranous  bands,  and  how,  at  the  same  time,  the  uranyl  acetone  bands  appear 
in  place  of  the  uranous  bands. 

Plate  39,  A,  strip  1,  represents  the  absorption  of  uranous  chloride  in 
equal  parts  of  water  and  methyl  alcohol.  Strip  2,  the  same,  to  which  is  added 
a  solution  of  sodium  perchlorate  in  water  and  methyl  alcohol.  Strip  3  is  a 
corresponding  strip  when  sodium  perchlorate  is  replaced  by  potassium  chlorate 
in  4  parts  of  water  and  3  of  methyl  alcohol.  Strip  4  is  the  absorption 
of  a  solution  of  uranous  chloride  in  methyl  alcohol  and  ether.  Strips  2  and 
3  show  quite  a  strong  selective  action  of  these  salts  in  increasing  the  relative 
intensity  of  the  alcohol  bands.  This  action  is  especially  marked  in  the  case 
of  potassium  chlorate. 

Plate  39,  B,  strip  1,  represents  the  absorption  of  uranous  chloride  in  equal 
parts  of  water  and  methyl  alcohol,  to  which  calcium  nitrate  is  added;  the 


SPECTROPHOTOGRAPHY  OF  CHEMICAL  REACTIONS.  69 

latter  being  dissolved  in  2  parts  of  water  and  3  parts  of  methyl  alcohol  in 
strip  1 ;  in  1  part  water  and  1  part  methyl  alcohol  in  strip  2,  and  in  pure  water 
in  strip  3.  Strips  4,  5,  6  represent  the  absorption  of  uranous  chloride  in  equal 
parts  of  water  and  methyl  alcohol,  to  which  potassium  nitrate  is  added;  in 
strip  4,  potassium  nitrate  is  in  2  parts  water  and  3  parts  of  methyl  alcohol, 
strip  5  in  equal  parts  of  water  and  methyl  alcohol,  and  in  strip  6  in  pure  water. 
The  last  strip  represents  the  absorption  of  uranous  chloride  in  equal  parts  of 
water  and  methyl  alcohol.  This  spectrogram  indicates  that  the  action  of  the 
calcium  and  potassium  nitrates  may  be  that  of  driving  back  the  amount  of 
hydrate  in  equilibrium  with  the  alcoholate,  and  that  by  increasing  the  pro- 
portion of  water  present  in  the  solution  the  amount  of  hydrate  present  is 
increased  at  the  expense  of  the  alcoholate. 

THE    REDUCTION    OF    URANYL   SALTS   IN    SOLUTION. 

The  reduction  of  uranyl  to  uranous  salts  deserves  a  thorough  study,  and 
undoubtedly  offers  a  fertile  field  for  investigation,  and  this  partly  on  account 
of  the  light  that  quantitative  spectrophotography  will  probably  throw  upon 
the  subject.  In  certain  solvents  some  interesting  results  have  already  been 
obtained.  In  the  case  of  an  ether  solution  of  uranyl  chloride  it  was  found  that, 
on  the  addition  of  zinc  and  hydrochloric  acid,  three  phases  resulted — an  oily 
and  extremely  concentrated  solution  of  uranous  chloride  formed  at  the  bottom; 
a  much  more  dilute  solution  of  uranous  chloride  which  was  above  the  oily 
layer  and  which,  on  standing,  gave  up  its  uranous  salt  to  the  oily  liquid 
below;  and  the  upper  layer,  which  only  contained  uranyl  chloride  in  solution. 
These  three  liquid  layers  were  completely  separate  from  one  another.  When 
the  whole  system  was  thoroughly  shaken  and  allowed  to  stand,  the  three 
strata  soon  separated  again  from  one  another. 

Uranyl  chloride  dissolved  in  isobutyl  alcohol,  to  which  zinc  and  strong 
hydrochloric  acid  are  added,  also  shows  the  formation  of  an  oily  and  dense 
liquid,  which  was  almost  opaque  on  account  of  the  large  amount  of  uranous 
chloride  dissolved  in  it.  These  very  concentrated  solutions  of  uranous  salts 
would  serve  admirably  for  low-temperature  work,  and  for  the  detection  of 
the  Zeeman  effect. 

When  hydrochloric  acid  is  added  to  a  solution  of  uranyl  chloride  in  propyl 
alcohol,  the  two  solutions  mix.  Zinc  is  then  added  and  the  reduction  takes 
place  very  slowly. 

A,  plate  26,  represents  the  absorption  spectrum  of  the  uranous  chloride 
solution  in  ether,  to  which  some  hydrochloric  acid  had  been  added.  The 
absorption  spectrum  is  quite  characteristic,  and  shows  some  new  bands. 
Several  of  these  bands  are  quite  sharp  and  narrow.  As  an  example,  there  is 
a  band  near  X  5000  that  is  quite  strong  and  is  only  about  25  Angstrom  units 
in  width. 

REDUCTION  OF  URANYL  CHLORIDE  IN  METHYL  ESTER. 

To  a  solution  of  uranyl  chloride  in  methyl  ester  were  added  hydrochloric 
acid  and  metallic  zinc.  The  hydrochloric  acid  does  not  mix  with  the  ester 
solution.  For  a  considerable  time  hydrogen  is  given  off,  the  ester  solution 
remaining  of  a  greenish-yellow  color.  Quite  suddenly,  however,  the  ester 


70  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

loses  its  greenish-yellow  color  and  becomes  slightly  clouded,  the  solution  being 
of  a  pale-white  color.  At  the  same  time  an  almost  black  solution  is  formed, 
whose  volume  is  about  the  same  as  that  of  the  hydrochloric  acid  added. 
Further  addition  of  hydrochloric  acid  results  in  the  ester  solution  becoming 
of  a  darkish-green  color,  while  a  small  amount  of  the  very  deeply  colored, 
oil-like  solution  still  remained  at  the  bottom  of  the  solution. 

SELECTIVE   REDUCTION    OF    URANYL   AGGREGATES 

The  method  employed  for  the  preparation  of  uranous  salts  for  work  on  their 
absorption  spectra  has  usually  been  to  add  an  acid  corresponding  to  that  of  the 
uranyl  salt,  and  some  zinc.  There  would  be  present  in  the  solution  of  the 
uranous  salt  the  corresponding  zinc  salt.  It  is  possible,  under  these  conditions, 
to  obtain  fairly  concentrated  solutions  of  uranous  chloride,  uranous  bromide, 
and  uranous  sulphate.  It  does  not  seem,  by  this  method,  to  be  possible  to 
obtain  uranous  nitrate  in  stable  condition.  A  small  amount  of  uranous 
nitrate  is  formed,  but  it  is  very  quickly  oxidized  again.  Dilute  aqueous 
solutions  of  uranous  acetate  can  be  obtained  by  this  method. 

The  most  concentrated  solution  of  any  uranous  salt  thus  far  obtained 
is  that  of  uranous  chloride.  A  considerable  volume  of  a  solution  of  uranyl 
chloride  in  ether  was  prepared;  to  this  was  added  a  small  amount  of  concen- 
trated hydrochloric  acid  and  zinc.  The  uranous  chloride  formed  is  nearly 
insoluble  in  the  ether,  and  collects  in  a  dark,  oily  liquid  at  the  bottom  of  the 
vessel. 

The  action  of  certain  acids  on  the  uranyl  salts  is  peculiar.  As  has  been 
stated,  the  addition  of  nitric  acid  and  zinc  to  a  uranyl  chloride  solution  did 
not  result  in  the  formation  of  any  uranous  salt,  although  the  absorption 
spectra  would  probably  have  shown  very  little  effect  on  the  uranyl  chloride 
bands  produced  by  the  addition  of  nitric  acid.  The  sulphate  would  probably 
have  been  a  better  uranyl  salt  to  use  in  this  connection,  because  the  uranyl 
sulphate  bands  are  harder  to  change  to  the  nitrate  bands  then  the  uranyl 
chloride  bands  are.  To  a  uranyl  chloride  solution  containing  some  free  hydro- 
chloric acid  were  then  added,  as  before,  some  nitric  acid  and  zinc.  In  this  case 
some  uranous  salt  was  produced,  but  it  was  quite  unstable  and  was  quickly 
oxidized  again. 

On  the  other  hand,  to  an  aqueous  solution  of  uranyl  chloride  were  added 
some  hydrochloric  acid  and  zinc.  A  uranous  salt  was  formed,  but  in  a  few 
minutes  this  was  transformed  back  into  the  uranyl  condition  again.  This  is 
rather  unexpected,  since  it  would  be  thought  that  the  uranous  salt  would  be 
in  the  condition  of  the  chloride,  and  the  chloride  is  quite  stable.  To  an  aqueous 
uranyl  nitrate  solution  were  then  added  a  large  amount  of  concentrated  hydro- 
chloric acid  and  a  little  zinc.  The  solution  turns  green  during  the  first  few 
minutes  and  then  goes  over  to  the  uranyl  state,  although  hydrogen  gas  is 
being  rapidly  evolved.  Very  little  could  be  done  with  the  bromides  along  this 
line  on  account  of  the  liberation  of  bromine.  It  would  be  very  interesting 
to  find  how  much  the  uranyl  bromide  bands  are  changed  before  the  bromine 
gas  is  evolved,  since  this  would  give  the  condition  of  the  aggregate  when  it  is 
broken  up  and  bromine  evolved. 


SPECTROPHOTOGRAPHY    OF    CHEMICAL    REACTIONS.  71 

B,  plate  25,  is  a  spectrogram  giving  the  result  of  the  addition  of  a  large 
amount  of  acetic  acid  and  a  little  zinc  to  uranyl  chloride  dissolved  in  acetone. 
The  chemical  conditions  in  this  solution  are  quite  complex  and,  therefore, 
little  can  be  said  about  them.  The  composition  of  the  red  uranous  band  is 
quite  unique  in  this  case.  For  a  considerable  amount  of  the  solution  the  red 
band  resembles  that  of  the  red  glycerol  band  of  uranous  chloride.  On  decreas- 
ing the  amount  of  salt  the  band  breaks  up  into  four  very  weak,  diffuse  bands, 
resembling  more  or  less  the  aqueous  uranyl  chloride  bands.  The  extreme 
red  part  of  the  absorption  consists  of  a  triplet  with  the  central  and  strongest 
band  located  at  about  X  6750.  The  other  bands  are  approximately  at  X  6670 
and  X  6820.  The  uranyl  bands  are  exceptionally  strong,  as  will  be  seen  from 
the  spectrogram. 

DIRECT    SPECTROSCOPIC   EVIDENCE    FOR    THE    EFFECT    OF    MASS. 

According  to  the  law  of  Mass  Action  if  the  salts,  uranyl  chloride  and  cal- 
cium nitrate,  were  dissolved  in  water,  uranyl  chloride  and  uranyl  nitrate  would 
both  be  present  in  the  solution.  According  to  the  theory  of  aggregates  the 
addition  of  calcium  nitrate  should  shift  the  uranyl  chloride  bands  to  the  violet, 
while  the  addition  of  calcium  chloride  to  uranyl  nitrate  should  shift  the  uranyl 
nitrate  bands  to  the  red.  This  was  found  to  take  place. 

Preliminary  tests  showed  that  the  addition  of  calcium  nitrate  to  uranyl 
nitrate  caused  a  slight  shift  towards  the  violet.  It  appears,  therefore,  that 
calcium  has  very  little  effect,  it  being  only  the  acid  radicle  that  is  effective. 
The  result,  then,  is  what  would  be  expected  according  to  the  law  of  Mass 
Action — the  effect  of  adding  aluminium  chloride  to  an  aqueous  solution  of 
uranyl  nitrate  causes  the  same  shift  of  the  uranyl  bands  that  would  be  pro- 
duced if  uranyl  chloride  were  added. 

A  spectrogram  was  made  of  the  absorption  of  uranyl  nitrate  in  water 
that  showed  about  eight  of  the  uranyl  bands,  the  blue-violet  band  being  about 
300  Angstrom  units  in  width.  The  addition  of  a  concentrated  solution  of 
calcium  nitrate  increased  the  general  absorption  of  the  blue-violet  band  very 
greatly,  so  that  only  the  a,  b,  and  c  uranyl  bands  remained.  The  position 
and  general  appearance  of  these  bands  did  not  seem  to  be  changed.  Further 
work  of  this  kind  will  be  done. 

To  a  solution  of  uranyl  chloride  in  water  a  concentrated  solution  of 
calcium  nitrate  was  added.  The  uranyl  chloride  solution  showed  the  a,  b, 
and  c  bands,  and  the  blue-violet  band  was  about  400  Angstrom  units  in  width. 
The  addition  of  the  calcium  nitrate  caused  the  blue-violet  band  to  be  shifted 
towards  the  violet,  the  shift  being  greater  on  the  long  wave-length  edge  of 
the  band.  The  uranyl  bands  also  appear  to  be  shifted  towards  the  violet, 
although  in  this  particular  spectrogram  they  are  so  weak  that  they  can  hardly 
be  detected.  Work  of  this  kind  will  be  done  with  uranyl  sulphate  and  uranyl 
nitrate,  since  the  neutral  uranyl  sulphate  bands  are  quite  sharp.  The  addition 
of  the  other  salts  should  also  be  gradual. 

A,  plate  16,  represents  the  spectrophotographs  of  the  addition  of  increas- 
ing amounts  of  calcium  nitrate  to  a  uranyl  chloride  solution  in  water.  The 
spectrogram  shows  the  gradual  shifting  of  the  blue-violet  band  and  the 
decrease  in  intensity  of  the  uranyl  chloride  bands. 


72  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

B,  plate  16,  shows  a  spectrophotograph  of  the  changes  produced  in  a 
nitric  acid  solution  of  uranyl  chloride  to  which  increasing  amounts  of  a  concen- 
trated solution  of  aluminium  chloride  in  water  are  added.  The  spectrogram 
shows  the  very  great  increase  in  the  amount  of  the  ultra-violet  absorption 
on  the  addition  of  the  aluminium  chloride.  The  blue-violet  band  does  not 
appear  at  all.  The  uranyl  bands  are  shifted  slightly  towards  the  red,  and 
apparently  change  but  slightly  in  intensity.  The  change  from  the  first  to  the 
second  strip  is  brought  about  by  the  addition  of  three  drops  of  the  aluminium 
chloride  solution. 

Plate  17  is  to  show  the  different  effect  produced  by  adding  an  acid  and 
a  neutral  salt.  A  represents  the  absorption  of  uranyl  nitrate  in  nitric  acid 
to  which  hydrochloric  acid  is  added,  and  this  plate  can  be  compared  directly 
with  B,  plate  16.  B,  plate  17,  on  the  other  hand,  shows  the  effect  of  the 
addition  of  an  aqueous  solution  of  aluminium  chloride  to  an  aqueous  solution 
of  uranyl  nitrate. 

A,  plate  17,  shows  the  increase  in  the  ultra-violet  absorption.  The  great 
increase  is  in  the  intensity  of  the  middle  uranyl  bands,  whereas  in  the  case 
of  the  first  strip  the  intensity  of  the  various  uranyl  bands  was  much  more 
evenly  distributed.  A  very  small  amount  of  hydrochloric  acid  produced  a 
very  great  change  in  the  uranyl  bands.  The  addition  of  aluminium  chloride 
produces  a  much  more  gradual  change  in  the  position  and  character  of  the 
uranyl  bands.  It  produces  a  much  greater  change  in  the  ultra-violet  absorp- 
tion, causing  the  uranyl  bands  to  shift  towards  the  red  and  to  increase  very 
greatly  in  intensity. 

A,  plate  22,  shows  the  effect  of  the  addition  of  calcium  nitrate  to  an 
aqueous  solution  of  uranyl  nitrate. 


CHAPTER  V. 

EFFECT  OF  TEMPERATURE   ON   ABSORPTION   SPECTRA. 

The  purpose  of  the  work  on  absorption  spectra  at  high  temperatures 
was  to  obtain  some  knowledge  of  the  chemical  changes  that  take  place  at 
these  temperatures,  by  means  of  changes  produced  in  the  absorption  spectra. 
The  cells  used  have,  in  the  main,  been  the  quartz  cell  and  the  two  steel 
cells  described  in  a  previous  chapter.  Some  qualitative  observations  were 
made  with  a  hand  spectroscope  on  solutions  showing  water  and  alcohol 
bands.  The  work  done  with  the  quartz  cell  was  mainly  with  acid  solutions, 
and  this  was  done  with  a  view  to  testing  the  stability  of  acid  aggregates,  as 
will  be  explained  a  little  later.  Some  work  was  carried  out  on  the  change 
in  the  relative  intensities  of  various  solvate  bands  with  change  in  temperature. 
This  will  also  be  taken  up  in  detail. 

The  problem  has  been  found  to  be  a  very  difficult  one,  on  account  of 
closing  the  cell  tightly,  and  very  largely  because  of  the  formation  of  precipi- 
tates upon  the  windows  of  the  cell. 

Some  work  has  been  done  dealing  with  the  effects  of  pressure  and  high 
temperature  upon  solutions.  W.  N.  Ipatieff1  has  shown  that  under  a  pressure 
of  about  125  atmospheres  of  hydrogen,  anthracene  and  phenanthrene  were 
reduced,  when  heated  in  the  presence  of  nickel  oxide,  to  compounds  such  as 
C14H12,  C14HU,  C14H2o,  etc.  From  this  work  and  that  of  others  it  has  been 
shown  that  metals  are  precipitated  from  solutions  of  their  salts  by  hydrogen 
under  pressure.  There  appears  to  be  a  critical  temperature  for  the  precip- 
itation of  each  metal,  silver  and  mercury  being  precipitated  at  ordinary 
temperatures  under  a  pressure  of  200  atmospheres  from  a  decinormal  solution, 
while  copper  and  the  more  electro-positive  metals  could  not  be  precipitated 
even  when  the  pressure  exceeded  500  atmospheres.  At  120°  to  130°,  however, 
branched  crystals  of  copper  were  formed  at  100  atmospheres;  and  at  lower 
temperatures  cuprous  oxide  was  formed.  Cobalt  was  precipitated  at  180°  to 
200°,  nickel  at  200°,  lead  and  bismuth  at  240°  to  250°,  iron  at  400°  and  420 
atmospheres.  Ferric  oxide  was  precipitated  from  an  acetate  solution  at  350° 
and  230  atmospheres. 

Among  some  of  the  investigators  who  have  studied  the  effect  of  pressure 
and  temperature  on  the  conductivity  of  solutions  are  A.  Bogojawlensky  and 
G.  Tammann  in  1898,  and  F.  Korber2  in  1909.  In  most  cases  the  resistance 
decreased  as  the  pressure  increased,  but  in  many  cases  a  minimum  resistance 
is  reached,  after  which  a  further  increase  in  pressure  will  cause  an  increase 
in  the  resistance.  This  is  true  of  solutions  of  potassium  chloride  at  all  tem- 
peratures between  0°  and  100°  C.  At  0°  the  minimum  resistance  is  0.872  of  its 
original  value,  and  is  reached  at  3000  kg.  per  sq.  cm.;  at  100°  C.  the  minimum 
resistance  ratio  is  0.998  and  this  is  reached  at  900  kg.  per  sq.  cm.  Among 

1  Ber.  d.  chem.  Ges.,  41,  966  (1908);  42,  2078  (1909). 
Zeit.  phys.  Chem.,  67,  212  (1909). 

73 


74  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

halogen  compounds  the  largest  decrease  of  resistance  is  found  for  hydrogen 
chloride  (17  per  cent  for  y=100,  p  =  3000  and  <  =  19°  C.)  and  lithium  chloride 
(14  per  cent);  and  then  follow  potassium  chloride  (9),  sodium  chloride  (8), 
potassium  bromide  (6),  sodium  bromide  (5),  potassium  iodide  (2),  and  sodium 
iodide  (1). 

SOLVATES   AND   THE    EFFECT    OF    CHANGE    IN    TEMPERATURE    ON 
THE   RELATIVE   INTENSITY    OF   SOLVATE   BANDS. 

The  absorption  spectra  of  colored  salts,  in  general,  in  the  visible  region 
are  not  very  characteristic,  but  the  absorption  spectra  of  neodymium,  erbium, 
uranyl,  uranous,  and  a  few  of  the  other  rare-earth  salts  show  fine  characteristic 
bands,  more  or  less  distributed  throughout  the  spectrum.  There  are,  however, 
even  among  these  spectra,  very  few  cases  where  the  absorption  spectra  of  the 
same  salt  in  different  solvents,  or  of  different  salts  of  the  same  metal  in  the 
same  solvent,  are  very  different.  There  are,  however,  a  few  examples  of  well- 
defined  "solvent  bands,"  and  some  of  these  will  now  be  discussed. 

The  most  striking  examples  of  the  effect  of  the  solvent  on  absorption 
spectra  are:  those  of  water  and  ethyl  alcohol  upon  several  of  the  neodymium 
salts,  water  and  alcohol  upon  uranous  chloride  or  uranous  bromide,  and  water 
and  glycerol  upon  several  uranyl  and  uranous  salts.  The  spectra  may  well 
be  described  as  consisting  of  the  "  water, "  the  "  methyl  alcohol/ '  the  "  glycerol/ ' 
etc.,  bands  of  the  particular  salt.  When  the  salt  is  dissolved  in  a  mixture  of 
two  of  the  solvents,  both  sets  of  solvate  bands  appear,  and  if  the  solvents  are 
mixed  in  a  certain  proportion,  both  sets  of  bands  may  be  obtained  of  approxi- 
mately the  same  intensity.  The  intensity  of  any  set  of  solvate  bands  will  be 
proportional  to  the  amount  of  that  solvent  present.  As  the  amount  of  the 
solvent  present  is  changed,  the  solvate  bands,  in  general,  do  not  shift  their 
position,  but  only  change  in  intensity,  and  this  change  in  intensity  seems  to 
be  the  same  for  all  of  the  bands  characteristic  of  that  solvent.  Solvent  bands, 
in  this  respect,  differ  from  the  phosphorescent  bands  described  by  Lenard1 
and  Klatt. 

Just  as  a  characteristic  arc  or  spark  spectrum  has  been  regarded  as 
indicating  the  presence  of  a  certain  element,  just  so  a  characteristic  absorption 
spectrum  will  be  regarded  as  evidence  for  the  presence  of  a  compound;  and 
these  compounds  will  be  considered  as  being  composed  of  one  or  more  mole- 
cules or  ions  of  the  salt  ("aggregate")  and  one  or  more  molecules  of  the  sol- 
vent. On  account  of  the  definite  spectra,  we  shall  speak  of  the  "methyl 
alcoholate"  of  uranous  chloride,  the  "hydrate"  of  neodymium  bromide,  etc. 

Suppose,  for  instance,  that  the  number  of  radicles  in  an  aggregate  of  neo- 
dymium salt  molecules  and  ions  can  vary,  then  the  compound  in  which  absorp- 
tion takes  place  might  be  represented  symbolically  in  the  following  manner: 

s{UOi}y{UO,Cl,}*{a}a{CH,OH} 
and 

+ 
+ 

a/{Nd}y/{NdCU}g/{Cl}o/{CH,OH} 

1  Ann.  d.  Phys.,  31,642  (1910). 


EFFECT    OF    TEMPERATURE    OX    ABSORPTION    SPECTRA.  75 

In  most  cases  x,  x',  2,  and  z'  would  probably  be  small;  y  and  yr  may  also 
be  small,  and  if  hydrochloric  acid  or  some  other  chloride  is  present,  it  might 
be  possible  to  have  systems  of  the  following  composition: 

.  .  }z{Cl}a{CH3OH} 


The  absorption  may  be  due  to  some  condition,  possibly  one  of  internal 
ionization  of  the  aggregate,  and  as  long  as  the  number  of  aggregates  remains 
constant,  Beer's  law  will  hold.  Free  ions  may  split  off  from  the  aggregate 
without  the  character  of  the  absorption  being  greatly  changed.  It  might  be 
that  if  the  aggregates  were  completely  broken  up  into  their  constituent  ions 
and  molecules  no  characteristic  absorption  would  be  shown. 

In  this  case,  a  and  a'  may  either  be  considered  as  being  constant,  or  as 
being  so  large  that  the  atmosphere  of  the  solvate  around  the  absorber  is  so 
extensive  that  it  is  immaterial  whether  the  outer  solvent  molecules  are  present 
or  not.  On  account  of  the  fact  that  solvent  bands  coexist,  and  do  not  shift 
into  each  other  as  the  proportion  of  the  solvents  is  changed,  it  will  be  assumed 
that  at  least  the  inner  and  effective  solvent  molecules  are  all  of  one  kind  in 
any  "spectral"  compound. 

As  to  the  numerical  value  of  the  y's  the  absorption  spectra  of  course  do 
not  furnish  evidence.  The  phenomena  of  the  constancy  of  the  wave-length 
of  the  uranyl  sulphate  and  uranyl  nitrate  bands,  with  great  dilution  of  these 
salts,  leads  to  the  conclusion  that  in  this  case  at  least  the  value  of  y  is  greater 
than  unity.  Freezing-point,  boiling-point,  conductivity,  and  osmotic  pressure 
measurements  should  aid  in  determining  the  values  of  x,  y,  and  z  in  the  above 
equations. 

The  existence  of  complex  aggregates  of  the  above  kind  is  quite  rare  in 
inorganic  chemistry,  although  cases  have  been  known.  Our  own  work  on  the 
reduction  and  oxidization  of  certain  uranium  salt  and  acid  aggregates  has 
shown  that  these  different  aggregates  have  very  different  chemical  properties. 
Some  cases  of  a  series  of  a  similar  set  of  compounds  might  be  cited,  e.g.,  the 
cobaltamines.  A  large  number  of  cobaltamines  are  known,  and  these  have 
been  divided  into  six  series. 

The  diamine  series  [Co(NH3)2]X4Af.  In  this  series  X  =  NO2  and  M  is 
one  atomic  proportion  of  a  monovalent  metal,  or  the  equivalent  quantity  of 
a  divalent  metal.  These  salts  are  prepared  by  the  action  of  alkaline  nitrites 
on  cobaltous  salts  in  the  presence  of  a  large  amount  of  ammonium  chloride 
or  nitrate.  The  salts  are  yellow  or  brown  crystalline  solids,  and  are  not  very 
soluble  in  water. 

The  triamine  series  [Co(NH3)3]Z3.    X  may  be  Cl,  NO3,  NO,,  ^SO4,  etc. 

The  tetramine  series,  including, 

Praseo  salts  [R,Co(NH,)JX.     X  =  Cl. 
Croceo  salts  [(NO2)2Co(NH3)JX. 
Purpureo  salts  [RCo(NH3)4,H,0]X2. 
Roseo  salts  [Co(NH,)4(H,O)2]X3. 
Fuseo  salts  [Co(NH,)JOH.X2. 


76  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

For  the  methods  of  preparation  see  O.  Dammer's  Handbuch  der  anor- 
ganischen  Chemie,  vol.  3. 

The  pentamine  purpureo  salts  [RCo(NH3)5]Xj,  where  X  may  be  Cl, 
Br,  NO..,,  NO2,  3^SO4,  etc.  The  pentamine  nitrito  salts  are  known  as  the 
xanthocobalt  salts,  and  have  the  general  formula  [N02Co(NHs)5]X2.  The 
pentamine  roseo  salts  can  be  obtained  by  the  action  of  concentrated  acids  in 
the  cold  on  oxidized  solutions  of  cobaltous  salts.  They  are  of  a  reddish 
color.  On  heating  with  concentrated  acids  they  become  purpureo  salts. 

The  hexamine  or  luteo  series  has  the  composition  [Co(NH3)6]X3.  These 
salts  form  yellow  or  bronze-colored  crystals  which  decompose  on  boiling.  The 
above  examples  are  cited  because  the  cobalt  salts  give  an  absorption  band 
spectrum  in  some  cases  similar  to  the  uranyl  bands.  It  is  very  probable  that 
uranium,  neodymium,  erbium,  etc.,  give  rise  to  much  more  complex  com- 
pounds than  even  cobalt. 

It  will  be  assumed  that  the  absorption  bands  are  due  to  compounds  that 
represent  the  average  condition  of  the  given  dissolved  salt.  It  may  be  that 
only  a  few  of  the  particles  of  the  absorbing  salt  may  be  active  at  any  one 
instant.  For  instance,  Becquerel1  considers  that  only  a  very  small  number 
of  the  neodymium  atoms  are  taking  part  in  the  absorption  of  light  at  any 
moment.  It  may  be  that  the  absorption  only  takes  place  when  the  compound 
is  in  a  special  condition.  For  example,  in  the  case  of  the  uranyl  salts  we  may 
think  of  the  absorption  as  being  due  to  the  valency  electrons  in  the  UO2 
group.  The  absorption  may  take  place  when  one  of  these  electrons  leaves 
the  uranium  or  oxygen  atoms,  or  when  it  returns.  Whatever  the  mechanism 
may  be,  it  will  be  assumed  that  the  frequency  of  the  absorber  is  determined 
by  the  nature  of  the  compound  in  which  it  is  located,  and  that  this  compound 
is  typical  of  the  average  of  all  the  possible  compounds  in  the  solution.  Accord- 
ingly, if  the  "methyl  alcohol"  and  "water"  bands  of  uranous  bromide  dis- 
solved in  methyl  alcohol  and  water  are  of  approximately  the  same  intensity, 
it  follows  that  there  are  equal  amounts  of  the  uranous  bromide  existing  as 
the  "methyl  alcoholate"  and  as  the  "hydrate." 

In  the  case  of  neodymium  chloride  or  neodymium  bromide  Jones  and 
Anderson2  have  shown  that  the  "water"  and  "alcohol"  bands  are  of  about 
equal  intensity  when  the  solution  consists  of  8  per  cent  of  water  and  92  per 
cent  of  alcohol.  In  the  case  of  uranous  bromide  or  uranous  chloride  in  water 
and  methyl  alcohol,  it  is  found  that  the  "water"  and  "methyl  alcohol"  bands 
are  of  about  equal  intensity  when  there  are  approximately  2  parts  of  water 
to  3  parts  of  methyl  alcohol  in  the  solution.  In  the  case  of  the  neodymium 
salts  it  would  seem  that  the  "water"  bands  are  the  more  "persistent."  The 
less  "persistence"  of  the  "hydrate"  of  uranous  chloride  or  uranous  bromide 
may  be  due  to  the  presence  of  the  zinc  salts  formed  during  the  reduction  of 
the  uranyl  salts.  It  is  found  that  the  presence  of  free  hydrochloric  acid  in 
a  solution  containing  the  "hydrate"  and  "methyl  alcoholate"  of  uranous 
chloride  causes  the  "water"  bands  to  decrease  in  intensity  with  reference  to 
the  "methyl  alcohol"  bands.  The  action  of  any  chloride  would  probably  be 
the  same.  In  the  case  of  neutral  salts  of  neodymium  and  uranium  the  "  water ' ' 

1  Becquerel:  Le  Radium,  Sept.  (1907).  J  Phys.  Rev.,  26,  520  (1908). 


EFFECT    OF    TEMPERATURE    ON    ABSORPTION    SPECTRA.  77 

bands  are  usually  more  persistent  than  the  "glycerol"  bands,  and  these  in 
turn  are  more  persistent  than  the  "alcohol"  bands. 

In  the  case  of  neodymium  chloride  in  a  mixture  of  92  per  cent  alcohol 
and  8  per  cent  water  it  has  been  found1  that  Beer's  law  does  not  hold,  the 
"water"  and  "alcohol"  bands  being  of  about  equal  intensity  for  a  0.5  normal 
solution,  while  for  a  0.05  normal  solution  the  "water"  bands  are  much  stronger 
than  the  "alcohol"  bands.  Whether  the  "water"  bands  in  general  show 
such  a  "persistence"  is  being  investigated. 

On  the  other  hand,  it  has  been  found  that  the  "  alcoholates "  are  much 
more  "persistent"  than  the  "hydrates"  at  the  higher  temperatures.  This 
is  especially  pronounced  in  the  case  of  the  "water"  and  "alcohol"  bands  of 
uranous  chloride  and  uranous  bromide.  If  the  two  sets  of  bands  are  of  equal 
intensity  at  ordinary  temperatures,  at  80°  C.  the  "water"  bands  have  practi- 
cally disappeared.  This  observation  can  easily  be  verified  with  a  small  pocket 
spectroscope. 

Several  very  characteristic  spectra  have  been  obtained  for  neodymium 
salts  dissolved  in  isomeric  alcohols.  The  bands  of  neodymium  chloride  in  iso- 
butyl  alcohol  are  of  considerably  greater  wave-length  than  the  corresponding 
bands  of  neodymium  chloride  in  butyl  alcohol;  whereas  the  "propyl  alcohol" 
bands  are  displaced  to  the  red  with  reference  to  the  "isopropyl  alcohol"  bands. 
The  "butyl"  and  "isobutyl"  bands  of  neodymium  nitrate  are  very  much  alike, 
while  the  "propyl"  bands  are  displaced  to  the  red  as  compared  with  the  "iso- 
propyl" bands,  being  in  the  same  direction  as  for  the  chloride. 

NEODYMIUM  CHLORIDE  IN  WATER  AND  ETHYL  ALCOHOL. 

A,  plate  52,  represents  the  absorption  of  a  0.3  normal  solution  of  neo- 
dymium chloride  in  water  and  ethyl  alcohol.    The  temperature  range  is  from 
40°  to  80°  C.    The  original  film  shows  that  at  the  higher  temperatures  the 
water  band  X  4271  almost  disappears,  while  the  alcohol  band  becomes  stronger. 
The  e  group  shows  the  same  thing  in  a  general  way,  in  that  the  total  absorp- 
tion, especially  on  the  violet  side  of  the  band,  is  much  less  at  the  highest 
temperature  than  at  the  lowest  temperature. 

B,  plate  52,  shows  the  same  effect  for  a  more  dilute  solution.    The  finer 
water  bands  of  the  a,  6,  and  e  groups  are  shown  by  the  original  film  practically 
to  disappear  at  the  higher  temperatures,  while  the  alcohol  bands  become  more 
intense. 

NEODYMIUM  BROMIDE  IN  WATER  AND  METHYL  ALCOHOL. 

C,  plate  53,  represents  the  absorption  of  neodymium  bromide  in  water 
and  methyl  alcohol,  0.2  normal  and  1.0  cm.  length  of  cell.     The  variations 
in  temperature  were  from  30°  to  80°  C. 

In  the  lower  strip  the  alcohol  band  at  about  X  4285  hardly  appears  at  all, 
while  the  water  band  at  X  4271  is  quite  strong.  At  80°  the  water  band  is  still 
quite  strong,  and  the  alcohol  band  is  possibly  a  third  as  strong  as  the  water  band. 

NEODYMIUM  CHLORIDE,  BROMIDE,  AND  NITRATE  IN  WATER. 
B,  plate  55,  strip  1,  shows  the  absorption  of  a  2.05  normal  solution  of 
neodymium  chloride  in  water  at  20° ;  strip  2  is  the  same  at  50°,  and  strip  3  is 
the  same  at  75°. 

1  Phys.  Zeit.,  II,  671  (1910),  12,  269,  (1911). 


78  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

A,  plate  55,  represents  the  absorption  of  a  1.66  normal  aqueous  solution 
of  neodymium  bromide  at  20°,  40°,  60°,  80°,  and  93°,  the  highest  temperature 
being  that  represented  by  the  upper  strip. 

B,  plate  55,  strip  4,  represents  the  absorption  spectrum  of  a  2.05  normal 
aqueous  solution  of  neodymium  nitrate  at  20°,  strip  5  at  75°,  and  strip  6  at  95°. 

These  spectrograms  show  the  very  great  increase  in  the  absorption  of  the 
short  wave-lengths  as  the  temperature  reaches  about  90°.  The  spectrograms 
show  the  widening  of  the  individual  neodymium  bands.  There  is  a  slight  shift 
towards  the  red  with  rise  in  temperature,  but  this  is  very  small.  The  absorp- 
tion spectra  of  the  three  solutions  are  practically  the  same,  that  of  the  chloride 
and  bromide  being  nearly  identical,  while  that  of  the  nitrate  differs  a  little 
in  some  of  the  minute  details  of  the  individual  bands. 

NEODYMIUM  CHLORIDE  IN  METHYL  ALCOHOL. 

Plate  54,  A,  represents  the  absorption  of  a  0.1  normal  solution  of  neo- 
dymium chloride  in  methyl  alcohol,  10  cm.  depth  of  cell.  This  spectrogram 
shows  the  methyl  alcohol  bands  quite  sharply.  A  weak  band  appears  on  the 
first  strip  at  X  4015,  and  at  X  4200.  X  4285  is  quite  strong  and  only  about  10 
Angstrom  units  wide.  A  weak  and  quite  narrow  band  appears  at  X  4270. 
The  band  X  4270  is  rather  hazy;  X  4450  is  about  50  Angstrom  units  in  width 
and  is  very  diffuse,  its  red  side  not  being  as  diffuse  as  the  violet  side.  X  4620 
is  very  weak;  X  4700,  X  4770,  and  X  4820  all  have  about  the  same  intensity  and 
width,  the  first  two  being  accompanied  by  very  weak  bands  on  their  violet 
sides  at  X  4680  and  X  4750.  X  5040  is  very  weak  and  broad;  X  5120  is  about 
20  Angstrom  units  wide  and  is  very  strong.  X  5175  is  very  similar  to  X  5120, 
except  that  it  is  only  about  one-half  as  intense.  X5215,  X5250,  and  XQ5290  are 
all  very  intense  and  are  quite  sharp,  the  middle  band  being  about  20  Angstrom 
units  in  width,  while  the  other  two  are  only  about  10  Angstrom  units  wide. 
There  is  a  wide  absorption  band  from  X  5710  to  X  5940,  with  the  sharper  edge 
on  the  violet  side.  The  red  band  at  X  6850  appears  to  be  quite  strong  and 
about  20  Angstrom  units  in  width. 

The  other  strips  represent  the  same  solution  at  different  temperatures, 
these  being  15°,  26°,  40°,  55°,  78°,  and  85°,  starting  with  the  lowest  strip. 

With  rise  in  temperature  the  bands  all  become  somewhat  more  intense 
and  wider.  The  general  absorption  over  the  whole  spectrum  region  increases, 
especially  at  the  higher  temperatures,  and  begins  to  encroach  quite  rapidly 
in  the  violet  and  red  regions.  This  violet  absorption  is  probably  a  general 
absorption,  but  the  encroaching  on  the  red  side  is  probably  due  to  the  increase 
in  the  intensity  of  the  group  of  red  bands. 

In  the  upper  strip  transmission  extends  from  about  X  4200  to  X  6100. 
A  very  weak  band  appears  at  X  4200  and  a  very  weak  one  at  X  4305.  The 
bands  in  the  blue  and  green  have  changed  but  little.  Absorption  is  pretty 
complete  from  X  5100  to  X  5190,  X  5210  to  X  4350,  and  from  X  5690  to  X  5990. 
Weak  bands  appear  at  X  6230,  X  6280,  and  X  6750.  If  any  of  the  bands  showed 
any  shift  it  was  too  small  to  measure.  The  band  at  15°,  extending  from  X  5710 
to  X  5940,  widens  approximately  20  units  on  its  violet  side  and  50  units  on 
its  red  side.  It  is  probably  more  or  less  general  that  wide  absorption  bands 
usually  broaden  unsymmetrically  towards  the  red,  especially  when  this  side  is 
the  more  diffuse. 


EFFECT    OF    TEMPERATURE    ON    ABSORPTION    SPECTRA.  79 

A,  plate  53,  represents  the  absorption  of  a  methyl  alcohol  solution  0.2 
normal  and  with  1.0  cm.  depth  of  cell.    The  temperatures  are  25°,  40°,  55°, 
and  70°.    The  only  important  change  due  to  temperature  is  that  at  70°,  the 
intense  absorption  near  the  center  of  the  t  group  of  bands  having  practically 

disappeared. 

NEODYMIUM  BROMIDE  ix  METHYL  ALCOHOL. 

B,  plate  54,  represents  the  absorption  spectrum  of  a  0.1  normal  solution 
of  neodymium  bromide  in  methyl  alcohol.    The  length  of  cell  was  10  cm. 
The  temperatures  were  25°,  35°,  44°,  60°,  82°,  100°,  and  120°  C.,  beginning 
with  the  lowest  strip.    At  the  highest  temperature  a  slight  precipitate  was 
formed,  but  still  some  light  was  transmitted.    The  neodymium  solutions  all 
become  much  more  deeply  colored  at  the  higher  temperatures,  and  this  can 
easily  be  shown  by  heating  such  a  solution  in  an  ordinary  test  tube. 

The  absorption  spectrum  of  neodymium  bromide  in  methyl  alcohol  is 
quite  different,  as  far  as  minute  detail  goes,  from  that  of  the  chloride.  In 
general,  the  bands  of  the  chloride  are  from  5  to  15  Angstrom  units  farther 
towards  the  red  than  the  bromide  bands. 

For  the  lowest  strip,  very  weak  and  diffuse  bands  appear  at  about  X  4000, 
X  4180,  X  4600,  X  4900,  X  5040,  X  5320,  X  6230,  X  6260,  X  6730,  and  X  6790.  The 
ft  group  of  the  bromide  is  very  different  from  that  of  the  chloride.  It  consists 
of  a  very  sharp,  narrow  (3  units)  band  at  X  4265,  a  very  sharp  and  less  intense 
band  at  X  4275,  a  hazy  band  at  about  X  4280  which  more  or  less  overlaps 
X  4275,  and  at  higher  temperatures  X  4275  can  not  be  noticed  at  all.  A  very 
weak  band  appears  at  X  4300  and  a  broader  band  at  X  4325,  being  about  20 
Angstrom  units  in  width. 

The  7  group  of  the  chloride  is  also  quite  different  from  that  of  the  bromide, 
which  has  four  bands  of  almost  equal  intensity  at  XX  4690,  4745,  4765,  and 
4815.  Weak  bands  appear  at  X  4670,  X  4700,  and  X  4725.  The  5  group  consists 
of  a  rather  narrow  band  at  X  5090  and  a  very  strong  band  at  about  X  5115; 
a  lot  of  narrow  and  intense  bands  at  X  5200,  X  5220,  X  5235;  X  5250  and  X  5275 
practically  merge  into  a  single  band.  The  e  group  consists  of  a  single  wide 
band  extending  from  X  5700  to  X  5880. 

As  the  temperature  is  raised  the  violet  absorption  increases  quite  rapidly, 
and  the  8  and  e  groups  of  bands  become  wider  and  stronger.  The  latter  band 
widens  very  greatly  towards  the 'red.  All  the  bands  become  very  much  more 
diffuse.  This  is  particularly  true  of  the  ft  group,  since  at  120°  only  two  very 
hazy,  indistinct  bands  appear,  while  at  25°  some  of  the  bands  in  this  group 
were  almost  as  fine  as  spark  lines. 

No  measurable  shift  of  the  bands  towards  the  red  could  be  observed. 

That  the  absorption  spectra  of  the  chloride  and  the  bromide  in  methyl 
alcohol  should  be  so  different  was  quite  unsuspected,  since  these  two  salts 
have  almost  identically  the  same  absorption  spectra  in  aqueous  solution. 

NEODYMIUM  NITRATE  IN  ISOBUTYL  ALCOHOL. 

The  absorption  spectrum  of  a  solution  of  neodymium  nitrate  in  isobutyl 
alcohol  was  photographed  at  20°,  45°,  75°,  95°,  110°,  and  120°  C.  The  con- 
centration was  0.05  normal  and  the  depth  of  cell  10  cm.  The  first  strip  of 
this  spectrogram  is  described  under  the  chapter  on  the  mapping  of  spectra. 


80  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

The  general  result  of  rise  in  temperature  is  to  cause  a  large  increase  in  the 
general  absorption  in  the  ultra-violet.  This  is  especially  strong  at  120°,  where 
the  general  absorption  is  complete  to  about  X  4100,  and  extends  as  a  partial 
absorption  to  beyond  X5000.  The  neodymium  bands  are  considerably 
widened  by  rise  in  temperature,  and  are  shifted  in  many  cases  some  15  or  20 
Angstrom  units  towards  the  red  (120°  compared  with  20°). 

Some  of  the  more  pronounced  changes  may  be  noted  if  the  following 
wave-lengths  are  compared  with  those  described  under  the  chapter  on  map- 
ping of  spectra.  At  120°  a  weak  band  appears  at  X  4260.  It  is  about  10 
Angstrom  units  wide.  The  other  bands  of  the  /3  group  are  at  X  4295,  X  4305, 
X  4325,  and  X  4360.  The  lines  of  the  7  group  are  at  X  4725,  X  4775,  and 
X  4850.  The  8  group  consists  of  the  wide  band  at  X  5140  and  the  double  band 
at  X  5250  and  X  5275.  The  e  group  runs  from  X  5720  to  X  5960  as  a  single  band. 
NEODYMIUM  NITRATE  IN  ACETONE. 

A  spectrogram  was  made  of  the  absorption  spectrum  of  a  solution  of 
neodymium  nitrate  in  acetone,  in  the  long  cell,  at  16°,  40°,  70°,  100°,  and  180°. 
The  solution  became  opaque  at  about  110°,  and  afterwards  quite  transparent 
at  about  160°. 

The  effect  of  the  rise  in  temperature  was  to  cause  a  slight  shift  of  the 
neodymium  bands  to  the  red,  but  as  these  bands  were  so  very  broad  and  hazy, 
no  measurements  could  be  made.  The  strip  taken  at  180°  shows  a  very  great 
absorption  in  all  regions  except  the  yellow  and  red,  and  the  absorption  in  the 
red  is,  indeed,  almost  complete.  There  is  no  indication  of  any  neodymium 
bands  at  all,  so  that  it  seems  that  practically  all  the  neodymium  nitrate  had 
been  precipitated. 

ERBIUM  CHLORIDE  IN  WATER. 

A,  plate  60,  represents  the  spectrum  of  an  aqueous  solution  of  erbium 
chloride  at  20°,  30°,  85°,  and  115°  C. 

The  effect  of  rise  in  temperature  on  the  individual  erbium  bands  is  very 
small,  their  diffuseness  being  hardly  increased  with  rise  in  temperature.  The 
increase  in  the  general  absorption  throughout  the  region  of  smaller  wave- 
lengths is  enormous,  resulting  in  the  solution  being  practically  opaque  at  the 
higher  temperatures. 

Strip  1  shows  the  following  bands,  the  wave-lengths  being  only  approxi- 
mate: a  band  from  X  3430  to  X  3520;  a  strong  band  at  X  3540  which  is  about 
10  Angstrom  units  wide;  weak  bands  at  X  3555,  X  3570,  and  X  3595;  the  previous 
band  is  the  beginning  of  a  region  of  absorption  that  extends  to  X  3660;  a 
group  of  three  bands  that  practically  merge  into  a  single  band  running  from 
X  3750  to  X  3790;  weak  bands  at  X  3800  and  X  3840;  diffuse  bands  at  X  3870; 
strong  X  3900,  X  3950  weak,  X  4000  weak;  X  4045  sharp  and  narrow  (10  units)  ; 
X  3070  sharp  and  narrow;  X  4100  very  weak;  XX  4155,  4165,  4185,  4215— these 
bands  are  much  alike,  the  first  being  the  most  intense;  X  4270  is  wide  and  very 
weak;  X  4430  diffuse;  X  4450  very  weak;  X  4480  weak;  X  4500  strong;  X  4530  is 
apparently  covered  by  a  diffuse  band  on  its  red  side;  X  4685  weak;  X  4750  and 
X  4800  wide  and  weak;  X  4855  narrow;  X  4880  intense;  X  4930  probably  double; 
X  5200;  X  5225;  X  5245  intense;  X  5290  weak;  X  5380;  X  5390  weak;  X  5435; 
X  5455;  X  5520  weak;  group  at  X  5770  very  weak;  X  6440,  X  6460,  X  6530,  X  6560 
strong.  X  6600  and  X  6710  all  very  diffuse  and  having  a  very  "washed-out" 
appearance. 


EFFECT    OF    TEMPERATURE    ON    ABSORPTION    SPECTRA.  81 

URANYL  CHLORIDE  IN  ACETONE. 

A  spectrogram  was  made  of  the  absorption  spectrum  of  a  solution  of 
uranyl  chloride  at  22°,  40°,  60°,  170°,  185°,  and  195°.  At  about  70°  a  precip- 
itate was  formed,  but  the  solution  became  transparent  again  at  160°. 

At  22°  six  of  the  uranyl  bands  appear,  some  being  clearly  double,  as  is 
characteristic  of  the  acetone  bands.  At  40°  only  two  bands  appear,  the  general 
absorption  throughout  the  violet  and  blue  regions  of  the  spectrum  being  so 
great.  At  60°  no  uranyl  bands  appear  at  all,  the  short  wave-length  absorption 
extending  to  about  X  5500.  After  the  formation  of  the  precipitate  there  is 
quite  a  strong  transmission  in  the  violet  and  about  five  uranyl  bands  appear. 
The  uranyl  bands  are  weaker  and  considerably  narrower  at  the  higher  temper- 
atures. Above  60°  the  bands  appear  to  be  single.  From  170°  to  195°  the 
uranyl  bands  rapidly  decrease  in  intensity,  and  at  195°  they  are  so  weak  that 
one  can  not  be  certain  that  they  can  be  seen  at  all.  At  the  same  time  the  gen- 
eral absorption  in  the  violet  increases,  but  not  to  any  great  extent. 

URANYL  NITRATE  IN  PROPYL  ALCOHOL. 

B,  plate  64,  represents  the  absorption  of  a  0.005  normal  solution  of  uranyl 
nitrate  in  propyl  alcohol,  the  depth  of  cell  being  10  cm.  The  temperatures, 
starting  at  the  lowest  strip,  are  20°,  40°,  65°,  85°,  105°,  115°,  130°,  and  145°. 
The  sixth  and  seventh  strips  show  a  very  weak  transmission  on  the  violet 
side  of  the  blue-violet  uranyl  band.  At  145°  this  has  become  a  broad  region 
of  transmission.  This  spectrogram  shows  the  enormous  extension  of  the  gen- 
eral absorption  as  the  temperature  rises. 

The  first  strip  shows  the  uranyl  bands  X  4085,  X  4200,  X  4330,  and  X  4470. 

URANYL  CHLORIDE  AND  NITRATE  IN  ISOBCTYL  ALCOHOL. 

A,  plate  62,  represents  the  absorption  of  a  0.076  normal  solution  of  uranyl 
chloride  in  isobutyl  alcohol  at  20°,  60°,  85°,  and  115°  C. 

B,  plate  62,  represents  the  absorption  of  uranyl  nitrate  of  0.033  normal 
concentration  in  isobutyl  alcohol,  the  temperatures  being  20°,  50°,  80°,  100°, 
and  105°  C. 

In  the  case  of  the  chloride  solution  the  uranyl  bands  are  quite  strong  and 
fairly  sharp.  The  two  bands  that  show  are  at  X  4570  and  X  4730.  In  the  case 
of  the  nitrate  solution  only  a  single  band  at  about  X  4630  appears.  This  band 
is  very  diffuse  and  weak.  For  aqueous  solutions,  as  will  be  remembered,  the 
reverse  is  the  case,  the  chloride  bands  being  very  weak  and  diffuse  and  the 
nitrate  bands  being  quite  strong  and  narrow. 

URANYL  CHLORIDE  AND  NITRATE  IN  METHYL  ESTER. 

B,  plate  66,  represents  0.005  normal  solution  of  uranyl  nitrate  in  methyl 
ester  at  20°,  50°,  75°,  and  100°  C.  The  spectrogram  shows  that  the  uranyl 
bands  are  quite  strong  and  clear.  As  the  temperature  rises  the  general  violet 
absorption  increases,  and  the  uranyl  bands  are  slightly  shifted  towards  the 
red.  The  approximate  wave-lengths  of  some  of  the  bands  are  XX  3900,  4020, 
4130,  4250,  4380,  4520,  4670,  and  about  4820,  this  last  band  being  very  weak. 

B,  plate  63,  shows  uranyl  and  calcium  chlorides  in  methyl  ester  (first 
three  strips),  and  uranyl  and  calcium  chlorides  in  methyl  alcohol  (last  three 


82  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

strips).  The  temperatures  are  20°,  45°,  85°,  20°,  50°,  and  95°  C.  The  methyl 
ester  at  20°  showed  very  strong  bands  at  XX  4600,  4760,  and  4930. 

It  was  thought  that  by  adding  a  large  amount  of  a  salt  like  calcium 
chloride  to  solutions  of  uranyl  chloride  in  different  solvents  the  absorption 
spectra  of  the  resultant  solutions  would  be  more  alike.  The  spectrogram 
shows  that  this  is  not  the  case,  since  it  will  be  seen  in  the  lower  strips  that  the 
uranyl  bands  are  very  strong  and  quite  sharp,  whereas  in  the  case  of  the 
methyl  alcohol  solution  the  bands  are  very  wide  and  very  weak.  Their  wave- 
lengths are  also  considerably  greater  than  those  of  the  bands  in  the  ester  solu- 
tion. These  spectrograms  show  that  although  double  salt  aggregates  may 
be  formed,  the  solvent  part  of  the  aggregate  still  plays  a  very  important  rr.le 
in  influencing  the  wave-lengths  of  the  absorption  bands. 

The  effect  of  the  addition  of  calcium  chloride  to  the  ester  solution  was 
not  tested  by  regular  steps,  but  for  the  pure  uranyl  chloride  solution  the  a 
band  appears  as  a  double  band  with  the  components  at  about  X  4930  and 
X  4965.  These  bands  practically  merge  into  one  another,  and  it  is  rather 
difficult  to  see  that  the  band  is  really  double.  Apparently  the  effect  of  the 
addition  of  calcium  chloride  is  to  cause  the  component  X  4965  to  disappear, 
and,  at  the  same  time,  the  other  component  widens.  The  methyl  ester  solu- 
tions offer  a  promising  field  for  studying  the  spectrophotography  of  chemical 
reactions  and  also  for  the  effect  of  dilution. 

A,  plate  64,  represents  the  absorption  of  0.005  normal  solution  of  uranyl 
chloride  in  methyl  ester,  the  depth  of  cell  being  10  cm.  The  temperatures, 
starting  with  the  lowest  strip,  are  20°,  45°,  70°,  90°,  110°,  135°,  and  140°  C. 

At  20°  the  following  uranyl  bands  appear:  X  3930  fine  and  weak;  X  4050 
quite  narrow;  X  4170,  X  4300,  X  4450,  X  4630,  and  X  4800  probably  the  6  band. 
At  140°  C.  only  the  6,  c,  and  d  bands  appear  at  XX  4480,  4650,  and  4820.  At 
the  highest  temperature  the  transparency  of  the  solution  in  the  violet  has 
apparently  increased.  The  character  of  the  uranyl  bands  is  but  slightly 
affected  by  the  above  temperature  changes. 

URANOUS  CHLORIDE  IN  WATER  AND  METHYL  ALCOHOL. 

Strip  5,  A,  plate  67,  represents  the  absorption  of  uranous  chloride  in  a 
mixture  of  water  and  methyl  alcohol,  in  such  proportions  that  the  water  and 
alcohol  bands  were  of  about  equal  intensity  at  10°  C.  Strip  6  represents  the 
same  solution  at  about  70°  C. 

These  strips  show  that  at  the  higher  temperature  the  uranous  water 
bands  have  almost  disappeared.  The  uranyl  bands  have  also  become  very 
much  weaker,  and  the  uranous  alcohol  bands  slightly  weaker.  No  appreciable 
shifting  of  the  bands  is  to  be  noticed. 

URANOUS  CHLORIDE  IN  ACETONE. 

A  spectrogram  of  the  absorption  spectrum  of  uranous  chloride  in  acetone 
was  taken  at  20°,  40°,  65°,  80°,  95°,  and  105°. 

At  about  60°  a  precipitate  was  formed,  and  above  this  temperature  the 
red  absorption  band  hardly  appears  at  ail.  The  uranous  bands  in  the  green 
and  yellow  seem  to  be  considerably  stronger  after  the  formation  of  the  pre- 
cipitate. 


EFFECT    OF    TEMPERATURE    ON    ABSORPTION    SPECTRA.  83 

THE   EXISTENCE     OF     AGGREGATES     AND     THEIR     PROPERTIES,     AND 
THE    EFFECT    OF    RISE   IN    TEMPERATURE    ON    THE   AGGREGATES. 

The  presence  of  free  acid1  or  of  other  salts  has  been  found,  in  many  cases, 
to  modify  very  considerably  the  uranyl,  uranous,  and  neodymium  bands  of 
a  given  salt  in  solution.  Up  to  the  present,  work  of  this  kind  has  been  practi- 
cally restricted  to  aqueous  solutions,  although  similar  changes  take  place  in 
other  solvents.  One  of  the  most  pronounced  cases  is  that  of  the  uranyl  nitrate 
and  the  uranyl  chloride  bands.  Most  of  the  nitrate  bands  have  shorter  wave- 
lengths than  the  chloride  bands.  As  increasing  amounts  of  hydrochloric  acid 
are  added  to  an  aqueous  solution  of  uranyl  nitrate,  the  nitrate  bands  are  found 
to  shift  gradually  into  the  position  of  the  chloride  bands.  Furthermore,  the 
addition  of  nitric  acid  to  an  aqueous  solution  of  uranyl  nitrate  causes  most 
of  the  uranyl  bands  to  shift  towards  the  violet,  whereas  the  addition  of  hydro- 
chloric acid  to  an  aqueous  solution  of  uranyl  chloride  causes  most  of  the  bands 
to  shift  towards  the  red.  These  changes  are  quite  different  from  those  that 
take  place  when  the  solvent  is  changed;  and  if  it  is  supposed  that  a  character- 
istic absorption  spectrum  corresponds  to  a  more  or  less  stable  compound, 
then  these  changes  indicate  a  series  of  compounds  which  will  be  referred  to 
as  aggregates.  We  would  have,  then,  nitric  acid  aggregates  of  uranyl  nitrate, 
or  hydrochloric  acid  aggregates  of  neodymium  chloride. 

Whether  there  is  an  actual  change  in  the  frequency  of  vibration  for  a 
series  of  uranyl  or  uranous  aggregates,  or  whether  there  is  simply  a  relative 
change  in  the  intensity  of  a  number  of  finer  bands  which  blend  into  the 
rather  broad  and  diffuse  bands  that  are  photographed,  can  not  be  decided  at 
present.  In  the  case  of  neodymium  salts2  the  various  spectrophotographs 
indicate  the  latter  effect.  It  is  unlikely  that  the  case  can  be  settled  very  easily 
for  uranyl  and  uranous  salts,  since  the  greatest  shifts  take  place  in  the  absorp- 
tion of  aqueous  solutions,  and  these  can  not  be  studied  at  very  low  tempera- 
tures. Subsequently,  it  will  be  assumed  that  a  spectrogram  of  a  chemical 
reaction  showing  a  gradual  shifting  of  bands  indicates  the  presence  of  a  series 
of  closely  related  aggregates  existing  in  the  solution. 

The  mixture  of  varying  proportions  of  two  neutral  salts  in  a  solution  may 
result  in  a  gradual  change  from  the  bands  of  one  salt  into  the  bands  of  the 
other  salt  (mixtures  of  uranyl  nitrate  and  uranyl  chloride  in  water).  On  the 
other  hand,  there  are  cases  in  which  each  salt  seems  to  have  its  own  definite 
spectrum.  In  this  case  there  will  be  no  shifting  of  the  bands  but  only  a  change 
in  intensity,  and  we  may  assume  that,  in  this  case,  there  are  no  double  salts 
formed.  In  the  former  case,  however,  it  seems  probable  that  there  are  aggre- 
gates formed  which  contain  one  or  more  molecules  of  each  salt. 

The  addition  of  salts3  containing  the  same  cation  as  the  corresponding 
uranyl  or  uranous  salt,  has  an  effect  similar  to  that  of  the  addition  of  free 
acid,  and  may  be  considered  as  indicating  the  presence  of  aggregates.  In  the 
case  of  uranyl  chloride  the  effect  seems  to  be  due  largely  to  the  chlorine  present. 

Acid  aggregates  of  uranous  salts  are  found  to  be  much  more  stable  than 
the  neutral  aggregates.  Uranous  nitrate,  for  example,  is  very  unstable,  but 

1  Phys.  Zeit.,  11,  668  (1910),  12,  269  (1911). 

'Ibid.,  II,  671  (1910),  12,269  (1911). 

3  Publication  No.  130,  Carnegie  Institution  of  Washin<rton,  p.  91. 


84  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

uranous  chloride  dissolved  in  concentrated  nitric  acid  will  stand  for  hours 
before  it  is  oxidized  to  the  uranyl  condition.  Most  of  the  neutral  uranous 
salts  are  precipitated  when  heated  to  80°  or  90°  C.;  but  if  some  free  acid,  or 
if  in  the  case  of  uranous  chloride  other  chlorides  are  present,  the  uranous  salts 
are  stable  at  these  higher  temperatures. 

It  might  be  expected  that  if  the  effect  of  rise  in  temperature  is  to  break 
up  aggregates,  then  in  the  case  of  concentrated  acid  solutions  of  the  uranyl 
salts  the  shift  towards  the  red  should  be  very  great  for  a  concentrated  nitric 
acid  solution  of  uranyl  nitrate;  while  in  the  case  of  a  hydrochloric  acid  solu- 
tion of  uranyl  chloride,  or  of  a  sulphuric  acid  solution  of  uranyl  sulphate,  the 
shift  should  be  in  the  opposite  direction.  On  the  other  hand,  if  the  shift  caused 
by  change  in  temperature  is  due  to  some  other  cause  and  the  aggregates  are 
not  broken  up,  no  effect  of  this  kind  would  be  expected. 

In  a  solution  of  uranous  sulphate  in  sulphuric  acid  the  uranyl  bands  are 
slightly  shifted  to  the  red  as  the  temperature  is  raised  from  10°  to  90°,  while 
the  uranous  bands  are  slightly  shifted  to  the  violet.  The  shift  of  the  neutral 
uranyl  sulphate  bands  to  the  red  is  greater  than  that  of  the  acid  sulphate 
bands.  The  shift  of  the  uranyl  nitrate  bands  in  nitric  acid  is  about  15  Ang- 
strom units.  All  bands  are  shifted  about  the  same  amount. 

NEODYMIUM  SALTS  IN  ACID  SOLUTIONS. 

Plate  59,  A.  This  spectrogram  shows  the  effect  of  hydrochloric  acid, 
sodium  chlorate,  and  temperature  on  the  neodymium  chloride  bands.  Strip 
1  is  the  absorption  of  neodymium  chloride  in  water  at  about  10°,  strip  2 
the  same  at  about  90°.  Strip  3  represents  the  absorption  of  the  same  amount 
of  neodymium  chloride  in  concentrated  hydrochloric  acid  at  10°,  strip  4  the 
same  at  90°.  Strip  5  represents  the  absorption  at  10°  of  neodymium  chloride 
in  methyl  alcohol,  and  strip  6  the  same  containing  sodium  chlorate. 

Plate  59,  B.  This  spectrogram  shows  the  absorption  of  a  0.02  normal 
solution  of  neodymium  acetate  at  10°  in  strip  1  and  at  about  90°  in  strip  2. 
Strip  3  represents  the  absorption  of  a  small  amount  of  neodymium  chloride 
added  to  acetic  acid  so  as  to  fill  the  quartz  cell  at  10°,  and  strip  4  the  same  at 
90°.  Strip  5  represents  the  absorption  of  neodymium  acetate  in  acetic  acid 
at  10°,  and  strip  6  the  same  at  about  90°.  Strip  7  represents  the  absorp- 
tion of  a  solution  in  methyl  acetate  and  acetic  acid  at  10°,  and  strip  8  the 
same  at  90°. 

The  first  two  strips  in  A  show  that  the  effect  of  rise  in  temperature  on 
an  aqueous  solution  of  the  chloride  is  to  cause  a  very  slight  shift  of  the  bands 
towards  the  red,  and  to  give  them  a  much  more  diffuse  and  washed-out  appear- 
ance. The  hydrochloric  acid  solution  of  neodymium  chloride  shown  in  strips 
3  and  4  is  but  very  slightly  changed  by  rise  in  temperature,  and  there  is  no  indi- 
cation that  the  spectrum  becomes  more  closely  like  that  of  the  neutral  aqueous 
solution.  The  shift  to  the  red  is  very  small.  It  can  easily  be  noticed  for  the 
bands  of  the  e  group.  At  10°  the  long  wave-length  bands  of  the  d  group  are 
very  much  like  the  two  bands  of  the  neutral  aqueous  solution.  At  90°  these 
bands  have  both  become  very  diffuse,  blending  into  a  single  band,  and  the 
whole  center  of  the  band  is  greatly  shifted  towards  the  red.  This  is  the  great- 
est temperature  change  in  the  whole  spectrum.  The  presence  of  sodium 


EFFECT    OF    TEMPERATURE    ON    ABSORPTION    SPECTRA.  85 

perchlorate  in  a  methyl  alcohol  solution  of  neodymium  chloride  causes  the 
neodymium  bands  to  be  shifted  very  slightly  towards  the  violet. 

A  neutral  acetate  solution  in  water,  as  shown  in  strips  1  and  2  of  B,  is 
affected  like  the  neutral  chloride  solution,  in  that  at  the  higher  temperature 
the  bands  have  a  much  more  diffuse  washed-out  appearance.  This  is  especially 
true  of  the  a  group,  which  appear  very  weak  at  90°.  Very  little  shifting  of  the 
bands  towards  the  red  takes  place.  Strips  4  and  5  show  about  the  same  effect 
and  the  same  very  great  decrease  in  the  intensity  of  the  a  group  at  the  higher 
temperature.  In  the  next  two  strips  the  a  group  remain  of  about  the  same 
intensity  at  the  two  temperatures.  There  is  less  increase  in  the  diffuseness 
of  the  acetate  bands  in  acetic  acid  than  in  the  case  of  a  neutral  acetate  solution. 

Plate  56,  A.  This  spectrogram  represents  the  absorption  of  neodymium 
chloride  in  acetone  at  10°  (strip  1)  and  at  70°  (strip  2);  neodymium  chloride 
in  ether  at  10°  (strip  3;  a  precipitate  is  formed  at  higher  temperatures) ;  neody- 
mium chloride  in  ethyl  alcohol  0.02  normal  at  10°  (strip  4)  and  about  70° 
(strip  5) ;  neodymium  chloride  in  ethyl  alcohol  to  which  hydrochloric  acid  gas 
has  been  added  at  10°  (strip  6)  and  at  about  70°  (strip  7). 

Plate  56,  B.  This  spectrogram  represents  the  absorption  of  neodymium 
nitrate  in  nitric  acid  at  10°  (strip  1)  and  at  about  50°  (strip  2;  if  heated  to 
much  higher  temperatures  nitrous  oxide  is  formed) ;  of  neodymium  chloride  in 
methyl  alcohol  and  8  per  cent  of  water  at  10°  (strip  3)  and  at  about  70°  (strip 
4);  neodymium  nitrate  in  acetone  and  8  per  cent  water  at  10°  (strip  5)  and 
at  about  60°  (strip  6);  neodymium  chloride  in  60  per  cent  ethyl  alcohol  and 
40  per  cent  water  at  10°  (strip  7) ;  and  neodymium  chloride  in  40  per  cent 
water  and  60  per  cent  glycerol  at  10°  (strip  8). 

The  acetone  solution  of  neodymium  chloride  shows  very  little  if  any 
change  with  rise  in  temperature.  The  ethyl  alcohol  solution  shows  a  small 
increase  in  the  diffuseness,  and  a  very  great  shift  of  the  intensity  of  the  band 
groups  with  rise  in  temperature.  When  hydrochloric  acid  is  present  there  is 
very  little  change  of  this  kind.  The  new  and  very  strong  bands  appear  at 
about  X  3590  and  X  3750,  the  latter  band  being  about  50  Angstrom  units  wide. 

The  nitric  acid  solution  of  neodymium  nitrate  shows  very  little  change  in 
the  absorption  spectrum  with  rise  in  temperature.  The  bands  become  some- 
what more  diffuse  and  decrease  in  intensity.  The  red  bands  do  not  show  in 
the  strips.  Strips  3  and  4  show  the  very  considerable  increase  of  the  alcohol 
bands  over  the  water  bands.  The  a,  /3,  and  5  fine  water  bands  have  practically 
disappeared  at  the  higher  temperature. 

URANOUS  SULPHATE  IN  SULPHURIC  ACID. 

Plate  67,  A.  The  absorption  of  uranous  sulphate  in  sulphuric  acid  at  10° 
is  represented  in  strip  1,  and  at  about  90°  in  strip  2.  The  absorption  of  the 
neutral  uranous  sulphate  in  water  at  10°  is  shown  in  strip  3,  and  at  about 
90°  in  strip  4.  The  absorption  of  uranous  chloride  in  water  and  in  methyl 
alcohol  at  10°  is  shown  in  strip  5,  and  at  about  70°  in  strip  6.  The  uranyl 
bands  of  the  sulphuric  acid  solution  are  shifted  towards  the  red  with  rise  in 
temperature,  whereas  the  uranous  bands  seem  to  be  shifted  slightly  towards 
the  violet. 


86  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

URANYL  NITRATE  IN  NITRIC  ACID,  URANYL  CHLORIDE  IN  HYDROCHLORIC  ACID, 
AND  URANYL  SULPHATE  IN  SULPHURIC  ACID. 

Plate  67,  B.  The  absorption  of  uranyl  nitrate  in  nitric  acid  at  10°  is  rep- 
resented in  strip  1,  and  at  about  70°  in  strip  2;  of  uranyl  chloride  in  hydrochlo- 
ric acid  at  10°  in  strip  3,  and  at  about  80°  in  strip  4;  of  uranyl  sulphate  in  water 
at  10°  in  strip  5,  and  at  about  80°  in  strip  6;  of  uranyl  sulphate  in  sulphuric  acid 
at  10°  in  strip  7,  and  at  about  70°  in  strip  8. 

Every  one  of  the  uranyl  nitrate  bands,  due  to  the  rise  in  temperature, 
seems  to  be  shifted  about  10  Angstrom  units  towards  the  red,  the  uranyl 
chloride  bands  in  hydrochloric  acid  being  shifted  about  15  Angstrom  units. 

In  the  case  of  uranyl  sulphate,  only  the  uranyl  bands  in  the  region  of 
the  blue-violet  band  were  greatly  shifted  towards  the  red  with  rise  in  tem- 
perature. The  shift  seemed  to  be  considerably  greater  for  the  neutral  than 
for  the  acid  solution. 

According  to  the  aggregate  theory  we  might  expect  that  if  the  uranyl 
nitric  acid  aggregates  break  down  at  the  higher  temperatures,  the  uranyl 
bands  would  be  very  greatly  shifted  towards  the  red  on  account  of  less  nitric 
acid  molecules  affecting  the  uranyl  vibrations.  But  this  does  not  seem  to  be 
the  case  to  any  very  great  extent,  since  here  the  shift  to  the  red  is  not  any 
greater  than  for  the  other  uranyl  bands,  and  seems  to  be  about  the  same  for 
each  one  of  the  bands.  It  may  be  considered  that  the  hydrate  is  more  simple, 
however,  and  that  this  allows  more  of  the  nitric  acid  molecules  to  come  within 
the  range  of  the  absorbing  centers,  and  this  might  in  a  way  counteract  the 
effect  of  any  decomposition  of  aggregates.  Whether  the  effect  of  an  increase 
in  the  number  of  molecular  collisions  brings  a  greater  number  of  nitric  acid 
molecules  within  the  effective  range  of  the  absorbing  centers,  and  has  an 
effect  on  the  frequency,  can  not  be  decided  from  the  spectrograms. 

The  very  considerable  shift  of  each  one  of  the  uranyl  chloride  bands  of 
the  hydrochloric  acid  solution  towards  the  red  with  rise  in  temperature 
probably  indicates  that  there  is  very  little  decomposition  of  the  uranyl  acid 
chloride  aggregates. 

Since  apparently  only  the  e,  f,  g,  and  h  uranyl  sulphate  bands  are  greatly 
shifted  towards  the  red,  we  might  assume  that  there  is  a  slight  decomposition 
of  the  uranyl  sulphate  aggregates,  and  this  counteracts  what  we  might  call 
the  normal  temperature  shift. 

In  the  above  strips  temperature  has  very  little  effect  on  the  uranyl  bands, 
except  a  shifting  of  their  wave-lengths  towards  the  red. 


CHAPTER  VI. 

SUMMARY    AND    GENERAL    DISCUSSION    OF    THE     MOST 
IMPORTANT    RESULTS. 

MAPPING    OF    SPECTRA. 

The  first  problem  to  be  solved  in  a  study  of  absorption  spectra  is  the 
recording  of  the  spectra  themselves.  The  method  employed  in  this  series  of 
investigations  is  that  of  photographing  the  absorption  spectrum  of  a  solution 
placed  in  a  beam  of  light  having  a  continuous  spectrum.  Such  a  photograph 
may  be  called  a  spectrogram  or  a  map  of  the  given  absorption  spectrum. 

The  study  of  the  spectrograms  of  colored  solutions  shows  that  this  color 
is  due  to  a  selective  absorption  of  the  solution  in  some  part  of  the  spectrum, 
and  the  extent  of  this  selective  absorption  may  be  over  regions  of  the  spectrum 
hundreds  of  Angstrom  units  in  width,  or  over  regions  only  a  fraction  of  an 
Angstrom  unit  wide — a  width  that  is  not  much  greater  than  that  of  a  spark 
or  arc  line.  In  fact,  bands  of  almost  all  widths  and  degrees  of  diffuseness  are 
found  in  addition  to  the  absorption,  which  is  one-sided.  If  the  region  of  one- 
sided absorption  lies  in  the  red,  it  is  probable  that  it  has  another  edge  in  the 
infra-red.  Practically  all  solutions  show  an  encroaching  general  absorption 
in  the  ultra-violet  as  the  amount  of  the  solution  in  the  path  of  the  light  is 
increased  or  as  the  temperature  is  raised. 

The  plates  and  the  description  of  these  plates  in  Publications  Nos.  60, 
110,  130,  and  the  present  monograph  of  the  Carnegie  Institution  of  Washing- 
ton give  a  pretty  thorough  representation  of  the  details  of  the  absorption 
spectra  of  most  of  the  typical  solutions  of  the  colored  inorganic  salts. 

It  can  be  said,  in  general,  that  the  absorption  spectra  of  the  various  salts 
of  the  same  element  are  very  much  alike;  indeed,  so  much  alike  that  it  is  only 
when  considerable  dispersion  is  used  that  any  differences  can  be  noted.  It 
can  also  be  said  that  the  absorption  spectra  of  the  same  salt  in  various  sol- 
vents are  very  similar.  For  these  reasons  we  are  justified  in  assuming  that 
the  color  of  solutions  of  colored  salts  dissolved  in  colorless  solvents  is  due 
primarily  to  the  metal  or  metallic  radicle  of  the  colored  salt.  The  various 
spectra  that  are  characteristic  of  a  given  kind  of  salts,  say  the  uranous  salts, 
will,  therefore,  be  called  the  uranous  spectra. 

In  the  mapping  of  the  absorption  spectra  of  solutions  of  increasing  con- 
centration or  of  increasing  depth,  it  is  always  found  that  the  absorption  bands 
widen  and  become  more  intense  as  the  amount  of  salt  in  the  path  of  the  beam 
of  light  is  increased.  It  can  also  be  stated,  as  an  approximately  general  law, 
that  the  more  diffuse  a  band  is  the  greater  will  be  the  widening  under  these 
conditions.  Examples  of  this  kind  are  shown  by  the  uranous  bands,  which 
may  widen  from  fifty  or  a  hundred  Angstrom  units  to  a  width  of  thousands  of 
Angstrom  units.  The  widening  of  single,  very  sharp  bands  with  increasing 
amounts  of  the  salt  in  the  path  of  the  light  is  invariably  small.  As  an  example 
we  can  take  the  X  4271  neodymium  chloride  water  band. 

When  characteristic  absorption  spectra  of  salts  of  the  rare  earths,  of 
cobalt,  chromium,  etc.,  are  studied  with  the  use  of  a  high-dispersion  spectro- 

87 


88  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

scope,  it  is  found  that  the  finer  absorption  bands  are  different  for  the  same 
salt  in  different  solvents,  and  for  different  salts  in  the  same  solvent.  This 
difference  may  be  a  difference  in  the  number  of  the  bands  present,  a  difference 
in  the  intensity  and  width  of  the  bands,  or  a  difference  in  wave-length. 

It  can  be  said,  in  general,  that  the  absolute  differences  of  intensity, 
diffuseness,  and  wave-length,  under  these  conditions,  is  greater  for  the  larger 
and  the  more  intense  bands.  Unfortunately  the  very  large  bands  are  usually 
so  situated  in  the  spectrum  that  only  small  changes  in  the  amount  of  salt 
can  be  made  before  the  band  becomes  one-sided  on  account  of  the  compara- 
tively small  region  of  the  spectrum  that  can  be  investigated  by  photographic 
methods.  But  it  can  be  said  that  the  uranous  bands  show  greater  changes 
with  change  of  salt  or  solvent  than  the  uranyl  bands;  that  the  uranyl  bands 
show  greater  changes  than  the  neodymium  bands,  and  these  in  turn  seem  to 
show  much  greater  changes  than  the  dysprosium  and  samarium  bands;  and 
these,  in  turn,  probably  greater  changes  than  the  erbium  bands. 

When  we  consider  the  minute  structure  of  the  bands  and  groups  of  bands 
under  high  dispersion  we  find  very  great  differences,  especially  in  the  case  of 
neodymium.  The  different  salts  of  neodymium  in  the  same  solvent,  especially 
in  some  of  the  organic  solvents,  give  entirely  different  absorption  spectra. 
The  same  is  true  of  the  same  salt  in  different  solvents.  Isomeric  solvents  very 
often  show  characteristic  spectra.  The  absorption  bands  of  neodymium  have 
been  divided  into  groups  a,  |8,  7,  8,  e,  etc.  When  there  is  a  large  amount  of 
salt  in  the  path  of  the  beam  of  light,  each  group  usually  forms  a  single  broad 
band.  It  is  found  that  the  relative  intensities  and  characteristics  of  these 
groups  is  very  much  the  same  for  different  salts  in  different  solvents.  The 
minute  structure  of  the  bands  in  the  same  group  is  usually  more  widely 
different  than  the  absorption  spectra  of  dysprosium  and  samarium;  so  that 
it  is  quite  probable  that  if  the  region  of  spectrum  that  we  could  study  were  wide 
enough  to  include  one  of  these  groups  and  sufficient  dispersion  was  at  hand, 
we  would  consider  that  we  were  dealing  with  different  elements  whenever  the 
salt  and  the  solvent  were  changed. 

The  spectrograms  and  the  descriptions  in  detail  give  a  large  number  of 
examples  illustrating  the  above.  Very  much  more  work  of  this  kind  remains 
to  be  done  with  solutions  like  those  of  neodymium  at  low  temperatures,  using 
very  high  dispersion. 

From  the  above  description  of  absorption  spectra  it  follows  at  once  that 
any  law  such  as  the  supposed  law  of  Kundt,  connecting  the  wave-length  of 
the  absorption  band  with  the  value  of  the  dielectric  constant  of  the  solvent, 
is  impossible.  It  is  probable  that  the  so-called  Melde  effect  is  equally  chi- 
merical. Looked  at  from  the  point  of  view  of  the  aggregate  theory  the  Melde 
effect  has  very  little  if  any  meaning. 

Beer's  law  is  found  to  hold  approximately  for  nearly  all  solutions  of  a 
single  neutral  salt  in  a  single  solvent.  Exceptions  are  found  when  very  con- 
centrated solutions  are  used,  and  with  only  one  known  exception  (solutions 
of  uranyl  acetate  give  a  very  large  negative  deviation)  the  deviation  is  such 
that  the  absorption  is  greater  than  would  be  given  by  Beer's  law  when  the 
concentration  is  increased.  The  fact  that  Beer's  law  holds  indicates  that,  as 
far  as  our  knowledge  of  absorption  spectra  is  concerned,  there  is  no  difference 


SUMMARY    AND    GENERAL    DISCUSSION    OF    RESULTS.  89 

between  ions  and  molecules.  It  therefore  can  not  be  said,  in  general,  that  for 
solutions  showing  characteristic  bands  there  is  any  part  of  the  spectrum  due 
to  ions  or  any  part  due  to  molecules.  Yet  the  work  of  Jones  and  Anderson1 
showed  that  certain  bands  are  probably  due  to  certain  constituents  of  the 
molecules,  such  as  the  atom,  the  hydrate,  etc. 

A    THEORY    OF    ABSORPTION    SPECTRA. 

It  is  natural  to  try  to  correlate  as  many  spectra  as  possible,  and  this  has 
been  done  in  many  cases.  For  organic  compounds,  benzene  for  example,  it  is 
found  that  the  ultra-violet  absorption  spectra  in  the  gaseous,  in  the  liquid, 
and  in  the  dissolved  states  are  very  similar.  It  is  therefore  natural  to  endeavor 
to  test  colored  salts  in  the  same  way.  Unfortunately  no  metallic  salts  having 
a  characteristic  absorption  spectrum  can  be  obtained  in  the  gaseous  state. 
As  pure  salts,  in  solutions,  and  in  transparent  solids,  however,  the  absorption 
spectra  of  salts  of  the  same  element  are  very  much  alike  as  far  as  the  grosser 
structure  is  concerned.  None  of  the  vapors  of  the  metals  of  these  salts  can 
be  obtained  unaccompanied  by  the  effects  of  high  temperature  and  intense 
ionization.  It  is  for  this  reason  that  the  branch  of  spectroscopy  dealing  with 
the  absorption  spectra  of  inorganic  solutions  is  quite  completely  separated 
from  the  other  branches  of  spectroscopy. 

However,  a  study  of  other  branches  of  spectroscopy  will  be  of  considerable 
importance  in  helping  to  give  us  a  working  hypothesis  concerning  the  mate- 
rial centers  that  are  absorbing  or  emitting  light. 

An  emission  or  absorption  center  of  light  and  heat  will  be  defined  as  the 
smallest  particle  existing  by  itself  that  is  capable  of  emitting  or  absorbing  a 
given  characteristic  spectrum.  Until  proved  to  be  an  ion,  an  atom,  a  molecule 
or  an  aggregate  of  these  we  can  not  assume  that  the  division  of  matter  into 
emission  and  absorption  centers  is  at  all  identical  with  the  division  of  matter 
into  ions,  atoms,  and  molecules.  In  a  study  of  these  light  centers  one  of  the 
most  difficult  problems  that  confronts  us  is  the  complete  separation  of  indi- 
vidual light  centers,  and  it  is  owing  to  this  fact  that  our  knowledge  of  these 
light  centers  is  so  meager.  An  example  of  this  kind  might  be  taken  in  the 
more  or  less  independent  series  of  lines  as  classified  by  Kayser  and  Runge, 
Ritz,  and  others.  It  has  never  been  proved  that  there  are  separate  emitters 
and  absorbers  for  each  one  of  these  series  of  lines,  neither  can  it  be  said  that 
these  centers  correspond  to  atomic,  ionic,  or  molecular  units.  It  may  be  that 
each  series  of  lines  is  due  to.  a  system,  and  that  several  systems  are  joined 
together  to  form  an  absorption  or  emission  center,  but  that  these  systems 
can  not  exist  as  separate  units  and  still  act  as  light  centers.  The  same  con- 
dition probably  applies  to  the  systems  that  give  rise  to  the  simple  series  of 
fluorescent  bands  discovered  by  Wood,  so  that  there  would  not  be  a  different 
absorption  center  for  each  one  of  these  series  of  bands,  but  that  there  is  one 
type  of  absorbing  centers  that  contains  several  absorbing  systems  that  can  be 
separately  excited,  and  that  as  soon  as  the  absorbing  center  is  broken  into 
parts  it  loses  its  characteristic  absorption  spectrum. 

It  seems  quite  probable  that  many  of  the  systems  in  the  light  centers 
contain  electrons,  and  it  is  probable  that  it  is  these  electrons  that  give  the 

1  Publication  No.  110,  Carnegie  Institution  of  Washington. 


90  THE   ABSORPTION    SPECTRA    OF    SOLUTIONS. 

Zeeman  effect.  The  electrons  that  are  indicated  by  the  Zeeman  effect  of  arc 
and  spark  lines  are  but  slightly  affected  by  external  forces,  so  that  it  has  been 
very  generally  assumed  that  these  form  parts  of  systems  that  make  up  the 
fundamental  structure  of  the  ultimate  units  of  matter.  Indeed,  a  character- 
istic spectrum  has  been  used  as  defining  an  atom;  and,  in  general,  it  has  been 
found  that  a  characteristic  arc  and  spark  spectrum  accompanies  matter 
which,  according  to  other  physical  and  chemical  methods,  is  believed  to  be 
composed  of  exactly  the  same  atomic  units.  It  is  for  this  reason  that  the 
assumption  is  generally  made  that  the  absorption  and  emission  centers  of 
these  arc  and  spark  spectra  are  either  the  same  as  the  atoms  of  the  element, 
or  contain  one  or  more  atoms  of  the  element. 

In  making  an  assumption  of  this  kind  two  of  the  greatest  difficulties 
encountered  are  the  complexity  of  the  spectra  that  are  found  to  be  character- 
istic of  an  element  and  the  fact  that  the  light  centers  only  seem  to  exist,  or 
at  least  are  only  active  under  certain  conditions.  The  first  problem  is  answered 
by  supposing  that  if  the  light  center  corresponds  to  the  atomic  unit  of  matter, 
then  there  are  subatomic  systems  that  correspond  to  the  various  spectra. 
Very  little  evidence  of  such  subatomic  systems  is  at  hand,  yet  the  present 
theory  of  radioactivity  gives  very  strong  support  to  this  view  and  indicates 
that,  whenever  these  subatomic  systems  are  separated,  entirely  new  atomic 
units  are  formed,  and  that  one  atomic  unit  may  consist  of  several  smaller 
atomic  units.  The  second  problem  is  illustrated  by  many  examples,  a  good 
one  being  that  of  sodium.  The  sodium  atoms  exist  under  conditions  that 
make  them  parts  of  entirely  different  light  centers.  The  sodium  atom  may 
form  part  of  the  absorbing  or  emitting  centers  of  the  arc  or  spark  spectra, 
the  emitting  centers  of  a  certain  vacuum  discharge  spectrum,  the  absorbing 
centers  of  the  fine-banded  absorption  spectrum,  the  emission  centers  of  the 
fluorescent  spectrum,  etc.  The  sodium  atoms  may  also  exist  in  various  mole- 
cules and  be  perfectly  transparent  in  the  visible  part  of  the  spectrum.  Sug- 
gestions have  been  made  only  as  to  what  the  constitution  of  the  light  centers 
of  these  spectra  may  be,  and  these  suggestions  have  usually  been  based  on 
the  assumption  that  these  light  centers  consisted  of  atomic  or  molecular 
complexes. 

Most  light  centers  seem  to  be  formed  only  during  very  exceptional 
physical  and  chemical  conditions,  so  that  they  have  been  often  considered 
as  being  very  unstable;  and  that  an  atom  or  molecule  only  forms  a  part  of  a 
light  center  during  a  small  part  of  the  time.  This  view  is  strengthened  by  the 
theory  of  absorption  and  dispersion,  according  to  which  it  often  happens 
that  the  number  of  electrons  taking  part  in  the  absorption  or  emission  of 
light  is  much  less  than  the  total  number  of  atoms  or  molecules  present  in  the 
matter  that  is  either  emitting  or  absorbing  the  light.  Exactly  what  conditions 
are  necessary  for  producing  light  centers?  Some  evidence  has  been  accumu- 
lated which  indicates  that  these  conditions  may  be  furnished  by  the  dissocia- 
tion or  recombination  of  parts  that  form  complex  molecules.  These  are 
apparently  the  conditions  under  which  the  light  centers  of  the  fine  iodine, 
bromine,  sulphur,  chlorine,  etc.,  bands  exist. 

The  length  of  duration  of  the  fluorescent  and  phosphorescent  bands  of 
solids  and  liquids  furnishes  a  method  of  analysis  of  spectra  in  that  the  duration 


SUMMARY    AND    GENERAL    DISCUSSION    OF    RESULTS.  91 

of  different  bands  after  the  excitation  has  ceased  is  very  different.  No  relations 
have,  however,  been  found  between  fluorescence  and  phosphorescence  and  the 
conductivity,  so  that  the  current  theories  are  based  on  the  assumption  that 
the  light  centers  are  very  complex  molecular  aggregates  (Lenard  and  Klatt) 
and  that  the  dissociation  or  recombination  effects  take  place  within  these 
aggregates. 

The  absorption  spectra  of  organic  compounds  supports  the  view  that  the 
absorbing  centers  in  these  cases  are  generally  complex.  These  centers  are 
called  chromophores,  and  as  a  rule  they  form  only  a  part  of  the  molecular 
structure.  Unfortunately  the  absorption  spectra  of  chromophores  are  not 
characteristic,  so  that  the  whole  study  is  more  or  less  a  colorimetric  one. 
The  peculiar  conditions  under  which  the  absorption  centers  are  active  has 
been  assumed  to  be  the  same  as  those  accompanying  phenomena  that  are 
explained  by  the  theory  of  dynamic  isomerism,  and  consist  in  a  supposed 
change  of  the  interlinking  of  radicles  in  the  organic  compounds.  If  valency 
is  of  an  electromagnetic  nature,  a  condition  of  dynamic  isomerism  would  also 
be  a  condition  of  intramolecular  ionization. 

The  nature  of  the  absorbing  centers  of  inorganic  salt  solutions  is  probably 
somewhat  similar  to  the  absorption  centers  found  in  the  case  of  solutions  of 
organic  compounds,  the  phosphorescent  compounds  of  the  rare  earths  studied 
by  Goldstein,  Kowalski  and  others.  Every  characteristic  absorption  spectrum 
will  be  considered  as  evidence  for  the  existence  of  a  compound,  and  these 
compounds  will  be  called  aggregates  and  may  be  assumed  to  consist  of  one 
or  more  molecules  or  ions  of  the  dissolved  salt,  and  one  or  more  molecules  of 
the  solvent.  That  the  number  of  these  aggregates  seems  to  be  quite  large  is 
no  evidence  against  the  theory  of  aggregates,  since  there  is  no  reason  why 
an  element  like  uranium  should  not  form  a  very  large  number  of  compounds. 

As  a  typical  example  of  an  aggregate,  we  will  take  a  mixture  of  two  kinds 
of  dissolved  compounds  in  a  mixture  of  two  solvents.  Assuming  that  the 
U02  group  can  act  as  an  ion  and  that  it  carries  a  double  charge,  a  general 
formula  for  aggregates  would  be  the  following: 

+ 

o;{UO2SO4}7/{H2SO4}w{u62}t;{H}w{SO4}o{H2O} 


We  may  assume  that  at  ordinary  concentrations  u,  v,  w,  u',  v',  and  w' 
have  small  values.  Whenever  a  definite  and  characteristic  absorption  spectrum 
is  obtained  it  will  be  assumed  that  the  absorption  centers  are  aggregates  of 
a  definite  composition,  and  that  all  the  coefficients  in  the  above  equation  have 
a  definite  value. 

From  the  fact  that  absorption  centers  are  found  in  solids  such  as  the 
various  glasses  and  crystals,  it  must  be  assumed  that  the  existence  of  active 
absorption  centers  need  not  be  connected  with  any  conducting  particles.  On 
the  other  hand,  the  work  of  Becquerel  and  others  seems  to  indicate  that 
the  number  of  absorbing  centers  is  much  smaller  than  the  number  of  atoms 
present.  If  the  aggregates  are  very  complex  then  the  number  of  absorbing 
centers  would  be  much  less  than  the  number  of  molecules  of  the  colored  salt. 


92  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

This  would  probably  require  very  large  values  for  x  and  x',  and,  therefore, 
makes  this  view  improbable.  On  the  other  hand,  it  is  not  necessary  to  assume 
that  the  aggregate  is  an  active  light  center  all  the  time,  but  that  the  aggregate 
is  only  active  while  it  is  in  a  peculiar  condition.  This  peculiar  condition  may 
be  assumed  to  be  a  kind  of  internal  ionization,  somewhat  similar  to  that  which 
is  assumed  in  the  theory  of  dynamic  isomerism,  or  by  the  theory  of  Lenard 
and  Klatt.  For  instance,  electrons  may  pass  back  and  forth  within  the  UOa 
group,  or  between  the  U02  and  surrounding  groups.  The  system  whose  vibra- 
tions give  rise  to  the  uranyl  group  is  probably  located  in  the  uranyl  radicle, 
and  possibly  in  the  uranium  atom  itself.  When  an  electron  is  ejected,  or 
when  it  recombines  with  the  UO2  group,  it  may  be  considered  that  the  system 
absorbs  light  and  is  then  an  active  center.  When  this  absorption  takes  place, 
the  frequency  of  the  absorption  bands  and  their  width  and  intensity  will 
depend  on  the  structure  of  the  aggregate — i.e.,  on  the  values  of  x,  y,  u,  v,  w, 
and  a. 

In  a  spectroscopic  study  of  the  aggregates  found  in  salt  solutions,  it  may 
be  said  that  the  absorption  spectrum  indicates  only  a  condition  of  a  small 
part  of  the  salt.  In  other  words,  the  values  of  x,  y,  u,  v,  w,  a,  etc.,  may  be 
functions  of  the  time.  In  order  to  solve  this  problem  it  will  be  necessary  to 
study  the  nature  of  the  aggregates  by  other  methods;  and  if  widely  different 
methods  give  the  same  values  for  x,  y,  u  .  .  .,  etc.,  it  may  then  be  assumed 
that  the  value  of  these  variables  is  not  a  function  of  the  time. 

In  the  present  treatment  it  will  be  assumed  that  these  spectroscopic 
aggregates  represent  the  statistical  average  condition  of  the  dissolved  salt 
molecules,  and  although  these  aggregates  may  be  active  absorbing  centers 
for  a  small  part  of  the  time  it  will  be  assumed  that  the  difference  between  an 
absorbing  and  a  non-absorbing  aggregate,  if  such  there  be,  is  not  due  to  any 
change  in  the  values  of  x,  y,  u,  v,  w,  a,  etc.  The  intensity  of  a  given  absorption 
spectrum  will  be  assumed  to  be  a  measure  of  the  amount  of  the  aggregate 
present  in  the  solution  that  corresponds  to  the  given  absorption  spectrum. 
In  every  known  example  it  has  been  found  that  the  changes  in  the  values 
of  x,  y,  z,  a,  etc.,  produce  changes  that  indicate  that  each  characteristic  spec- 
trum is  due  to  a  system  whose  parts  form  one  organic  whole. 

SOLVATION. 

In  the  general  formula  for  the  structure  of  the  absorbing  centers,  the 
coefficient  of  the  solvent  part  of  the  compound  is  represented  as  being  con- 
stant. The  fact  that  in  the  examples  studied  each  solvent  is  characterized 
by  a  definite  absorption  spectrum,  and  that  a  salt  dissolved  in  mixtures  of 
varying  proportions  of  two  solvents  shows  only  two  definite  absorption  spectra, 
indicates  that  definite  compounds  of  salt  and  solvent  are  formed.  It  is  a  very 
remarkable  fact  that  one  solvent  spectrum  does  not  gradually  change  into 
the  other  solvent  spectrum,  but  that  only  the  relative  intensities  of  the  two 
spectra  vary  as  the  percentage  of  each  solvent  present  is  changed,  and  that 
for  a  certain  percentage  of  the  two  solvents  the  two  sets  of  solvent  spectra  are 
of  approximately  the  same  intensity. 

Taking  as  an  example  uranous  bromide  in  water  and  methyl  alcohol,  we 
have  an  equilibrium  of  probably  the  following  type : 


SUMMARY    AND    GENERAL    DISCUSSION    OF    RESULTS.  93 

x{UBr4}a{H20}  «=» y  { UBr, } 6 { CH3OH } 

The  variables  x  and  y  may  be  equal  and  both  may  be  very  small.  These 
quantities  will  be  taken  up  later  in  the  treatment  of  aggregates. 

The  fact  that  there  is  no  gradual  shifting  of  the  "water"  bands  into  the 
"alcohol"  bands  indicates  that  the  equation  representing  the  equilibrium 
is  not  of  the  type: — 

a{UBrJz{H20}*/{CH3OH} 

where  x  and  y  are  variable  and  depend  on  the  amount  of  water  and  methyl 
alcohol  present.  The  above  constancy  of  a  and  b  must  not  be  interpreted 
too  literally,  however,  as  it  may  be  that  in  the  "atmosphere"  of  solvent 
molecules  only  the  inner  molecules  are  effective.  In  this  case  the  constancy 
of  a  and  6  would  indicate  that  only  the  number  of  molecules  in  the  outer 
region  of  this  atmosphere  could  change,  or  could  consist  of  a  mixture  of  water 
and  alcohol  molecules.  Accordingly,  the  inner  solvent  atmosphere  consists 
of  but  a  single  kind  of  molecules. 

(1)  The  percentage  of  solvents  for  which  each  set  of  solvent  bands  has 
the  same  intensity  will  be  used  as  a  measure  of  the  "persistency"  of  the  given 
solvates.     The  "persistency"  of  any  given  solvate  will  vary  inversely  as  the 
proportion  of  that  solvent  that  is  necessary  for  the  bands  to  appear  of  a  given 
intensity.    Whether  there  is  any  relation  between  the  persistency  of  solvate 
bands  and  the  absolute  values  of  a  and  6  is  not  known. 

(2)  The  persistency  of  the  same  solvate  bands  for  different  salts  is  quite 
different.    In  the  case  of  neodymium  chloride  in  water  and  alcohol  the  bands 
are  of  the  same  intensity  when  8  per  cent  of  water  and  92  per  cent  of  alcohol 
are  present.    In  the  case  of  samarium  chloride  a  smaller  percentage  of  water 
is  required,  the  water  bands  of  samarium  chloride  having  a  greater  persistency 
than  the  water  bands  of  neodymium  chloride.    The  persistency  of  the  water 
bands  of  neodymium  nitrate  is  different  from  those  of  the  chloride.    In  the 
case  of  the  uranous  salts  the  water  bands  are  much  less  persistent,  the  water 
and  alcohol  spectra  being  of  about  the  same  intensity  when  there  is  about 
40  per  cent  of  water  and  60  per  cent  of  alcohol  present. 

(3)  The  persistency  of  the  bands  of  the  same  salt  in  different  solvents  is 
very  different.    In  general  the  "water"  bands  are  the  most  persistent  of  all  the 
solvent  bands  at  ordinary  temperatures. 

(4)  The  persistency  of  solvent  bands  depends  on  the  concentration  of  the 
solution.    Keeping  the  percentage  of  water  and  alcohol  constant,  it  is  found 
that  the  alcohol  bands  of  neodymium  chloride  and  of  the  uranous  salts  are 
relatively  more  persistent  for  the  greater  dilutions,  i.e.,  Beer's  law  does  not 
hold  for  solutions  containing  two  solvents. 

(5)  Although  it  has  not  been  shown  that  only  two  solvates  exist  in  the 
case  of  a  neodymium  salt  in  a  mixture  of  two  isomeric  solvents,  yet  there  are 
several  instances  where  the  absorption  spectra  of  the  same  salt  in  isomeric 
solvents  are  very  different.    A  marked  example  of  this  kind  is  that  of  neody- 
mium chloride  in  isobutyl  and  butyl  alcohols,  the  butyl  alcohol  bands  having 
the  shorter  wave-lengths.     On  the  other  hand,  the  corresponding  propyl 
alcohol  bands  -are  shifted  to  the  red  with  reference  to  the  isopropyl  bands. 
The  absorption  of  neodymium  nitrate  in  butyl  and  isobutyl  alcohol  is  very 
much  the  same. 


94  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

(6)  From  the  above  examples  it  must  be  remembered  that  because  the 
absorption  spectra  of  a  salt  in  two  different  solvents  prove  to  be  very  much 
the  same,  this  fact  is  not  an  argument  that  no  solvation  exists  in  the  two  cases. 

(7)  The  values  of  x  and  y  probably  have  a  very  considerable  effect  on  the 
nature  of  the  solvates,  but  even  under  these  conditions  the  little  work  that  has 
been  done  indicates,  for  cases  where  y  has  a  value,  i.e.,  where  there  are  other 
salts,  or  the  acid  corresponding  to  the  given  salt  is  present,  that  we  still  have 
the  constants  a,  b,  etc.,  although  these  may  have  a  different  value  from  what 
they  have  when  y  =  0. 

(8)  Very  little  work  has  been  done  on  the  change  in  the  persistency  of 
solvate  bands  when  foreign  salts  are  added  to  the  solution.    The  addition  of 
aluminium  and  calcium  chlorides  to  solutions  of  colored  chlorides  seems  to 
increase  the  persistency  of  the  alcohol  bands  relative  to  the  water  bands. 

(9)  The  selective  action  of  foreign  salts  on  solvates  is  shown  very  strik- 
ingly by  the  addition  of  oxidizing  agents  to  solutions  of  uranous  salts  in 
water  and  alcohol.     Substances  like  potassium  and  calcium  nitrates  and 
sodium  perchlorate  cause  the  water  bands  to  decrease  very  greatly  in  inten- 
sity.    The  alcohol  bands,  on  the  other  hand,  seem  to  remain  of  about  the 
same  intensity.     Whether  this  is  due  to  the  oxidization  of  the  hydrate  or 
simply  to  a  decrease  in  its  persistency,  can  not  always  be  stated.     Some  cases 
indicate  that  selective  oxidization  takes  place.     The  oxidization  of  hydrogen 
peroxide  affects  water  and  alcohol  bands  in  the  same  way. 

(10)  In  many  cases  the  solubility  of  a  salt  like  uranous  bromide  is  much 
less  after  alcohol  has  been  added  to  the  water  than  before.    Sometimes  pre- 
cipitates form  when  a  second  solvent  is  added,  and  in  some  cases  the  filtrate 
shows  the  presence  of  only  one  solvate,  whereas  before  the  precipitate  was 
formed  both  solvates  were  present.    This  may  be  denoted  as  selective  solvate 
precipitation. 

(11)  The  effect  of  rise  in  temperature  changes  the  relative  intensity  of 
the  solvate  bands  of  a  solution.    A  very  marked  example  of  this  kind  is  a 
solution  of  uranous  chloride  in  a  mixture  of  water  and  ethyl  alcohol  in  such 
proportions  as  to  show  the  water  and  alcohol  bands  of  the  same  intensity  at 
ordinary  room  temperatures.     Heat  the  solution  to  about  80°  C.  and  the 
water  bands  practically  disappear,  leaving  only  the  uranous  alcohol  bands  in 
the  spectrum. 

(12)  Whether  or  not  there  is  a  dynamic  equilibrium  of  solvates  is  not 
certain,  but  the  selective  action  of  foreign  salts,  the  effect  of  changing  the 
relative  quantities  of  the  solvents  and  of  changing  the  temperature,  would 
lead  us  to  believe  that  there  is  some  interchange  of  solvates  going  on.    The 
velocity  of  reactions  of  this  kind  may,  however,  be  comparatively  slow. 

THE  URANYL  AND  URANOUS  BANDS. 

The  uranyl  spectrum  consists  of  some  twelve  bands  starting  from  X  5000 
and  runs  into  the  ultra-violet.  Starting  with  the  long  wave-length  band 
they  have  been  designated  by  the  letters  a,  6,  c,  etc.  These  bands  form  a  series, 
the  distance  between  the  bands  decreasing  with  the  wave-length.  The  uranous 
bands  do  not  form  any  series,  and  resemble  the  uranyl  bands  only  in  their 
general  appearance.  The  uranium  bands  are  quite  wide  and  diffuse  as  com- 
pared with  the  erbium  and  neodymium  bands.  A  considerable  amount  of 


SUMMARY    AND    GENERAL    DISCUSSION    OF    RESULTS.  95 

confusion  has  been  caused  in  the  past  by  the  fact  that  most  of  the  uranous 
salts  contain  uranyl  salts  mixed  with  them,  and,  therefore,  their  absorption 
spectra  include  the  uranyl  bands.  The  complete  independence  of  the  two 
sets  of  bands  is  very  clearly  shown  on  spectrograms  of  the  absorption  spectra 
of  a  uranous  salt  as  it  is  gradually  oxidized  to  the  uranyl  salt  by  the  addition 
of  hydrogen  peroxide. 

(1)  A  problem  of  considerable  interest,  and  one  for  which  an  answer1  has 
been  partly  obtained,  is  the  complete  correlation  of  the  a,  6,  c,  etc.,  bands 
when  one  uranyl  salt  is  transformed  into  another  salt,  or  when  the  solvent 
is  changed.    Thus,  for  instance,  the  a  band  could  be  traced  from  the  nitrate 
to  the  sulphate,  acetate,  etc.,  and  also  for  these  salts  in  various  solvents.    It 
may  be  that  the  neodymium,  erbium,  and  samarium  bands  can  be  studied 
in  the  same  manner,  especially  at  low  temperatures.    The  results  of  such  a 
study  should  extend  very  greatly  our  knowledge  of  chemical  reactions. 

(2)  If  uranyl  chloride  and  calcium  nitrate  are  dissolved  in  water,  uranyl 
chloride  and  uranyl  nitrate  should  both  be  present  in  the  solution.    In  terms 
of  the  theory  of  aggregates,  then,  it  would  be  expected  that  the  addition  of 
calcium  nitrate  to  an  aqueous  solution  of  uranyl  chloride  would  cause  the 
uranyl  chloride  bands  to  shift  towards  the  violet.     On  the  other  hand,  the 
addition  of  aluminium  or  calcium  chloride  to  an  aqueous  solution  of  uranyl 
nitrate  should  cause  the  uranyl  nitrate  bands  to  shift  towards  the  red.    The 
experimental  results  verify  these  conclusions. 

Preliminary  spectrograms  showed  that  the  addition  of  calcium  nitrate 
to  an  aqueous  solution  of  uranyl  nitrate  caused  the  uranyl  nitrate  bands  to 
shift  slightly  towards  the  violet,  the  amount  of  the  shift,  however,  being  very 
small.  This  seems  to  show  that  calcium  itself  has  very  little  if  any  effect  upon 
the  absorption,  and  this  is  in  agreement  with  the  results  of  Becquerel  and 
others. 

(3)  When  an  acid  is  added  to  a  neutral  uranyl  salt  in  sufficient  quantity, 
this  salt  is  changed  to  a  salt  of  the  acid  added.    Up  to  the  present  no  quanti- 
tative study  of  the  strengths  of  acids  by  the  spectroscopic  method  has  been 
made,  but  by  means  of  radiomicrometric  measurements  this  method  should 
give  a  reasonably  accurate  means  of  measuring  the  relative  strengths  of  vari- 
ous acids,  especially  in  aqueous  solutions. 

(4)  The  modus  operandi  by  which  uranyl  salts  are  transformed  into 
uranous,  and  vice  versa,  is  not  known.    This  subject  has,  however,  been  dis- 
cussed in  the  chapter  dealing  with  the  spectrophotography  of  chemical  reac- 
tions.   It  seems  probable  that  there  is  not  the  usual  dynamic  equilibrium 
between  the  uranyl  and  uranous  salts 

AGGREGATES  AND  THEIR  PROPERTIES. 

(1)  The  presence  of  free  acid  or  of  foreign  salts2  has  been  found  to  change 
the  frequency  of  many  of  the  uranyl,  uranous,  and  the  neodymium  bands. 
At  present  our  knowledge  of  these  effects  is  practically  restricted  to  aqueous 
solutions,  although  similar  effects  are  known  to  occur  in  other  solvents.  An 
example  of  the  above  effect  is  that  of  the  uranyl  chloride  and  nitrate  bands. 

1  Publication  130,  Carnegie  Institution  of  Washington. 

2  Phys.  Zeit.,  11,  668  (1910),  12,  269  (1911). 


96  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

The  wave-lengths  of  the  uranyl  nitrate  bands  are  considerably  smaller  than 
those  of  uranyl  chloride.  This  has  been  shown  to  be  due  to  the  presence  of 
NO3  and  H2O  groups  in  the  absorbing  centers  of  the  nitrate  in  solution.  By 
adding  hydrochloric  acid  to  an  aqueous  solution  of  uranyl  nitrate,  the  uranyl 
nitrate  bands  shift  gradually  to  the  positions  of  the  uranyl  chloride  bands. 
The  addition  of  more  hydrochloric  acid  causes  most  of  the  uranyl  bands  to 
continue  to  shift  towards  the  red.  On  the  other  hand,  the  addition  of  nitric 
acid  to  an  aqueous  solution  of  uranyl  nitrate  causes  the  uranyl  bands  to  shift 
towards  the  violet.  We  thus  obtain  a  gradual  shifting  of  the  uranyl  bands  of 
a  nitric  acid  solution  of  uranyl  nitrate  into  the  position  of  the  uranyl  bands 
of  uranyl  chloride  dissolved  in  concentrated  hydrochloric  acid.  The  magni- 
tude of  this  shift  is  shown  by  the  following  wave-lengths : 


Uranyl  bands. 

Nitrate  in  nitric  acid  
Chloride  in  hydrochloric  acid  

4790 
4950 

4670 
4800 

4510 
4635 

4370 
4450 

4125 
4280 

4000     3900 
4050     4015 

These  changes  are  quite  different  as  compared  with  those  that  take  place 
when  the  solvent  is  changed,  and  if  it  is  assumed  that  every  characteristic 
absorption  spectrum  corresponds  to  a  more  or  less  stable  system,  then  the 
above  changes  indicate  the  existence  of  a  series  of  systems  or  compounds. 
These  compounds  will  be  called  aggregates.  There  will  be,  accordingly, 
nitric  acid  aggregates  of  uranyl  nitrate,  uranyl  nitrate  and  chloride  aggregates, 
and  hydrochloric  acid  aggregates  of  uranyl  chloride. 

(2)  Whether  there  is  a  gradual  change  in  the  frequency  of  vibration  of 
the  absorbers  for  a  series  of  uranyl  or  uranous  aggregates,  or  whether  there 
is  simply  a  relative  change  in  the  intensity  of  a  number  of  finer  bands  which 
blend  so  as  to  form  the  uranyl  or  uranous  bands,  can  not  be  decided  from  the 
data  now  in  hand.    In  the  case  of  the  neodymium  salts,  the  latter  effect  seems 
to  manifest  itself  in  the  spectrograms  that  have  been  made. 

(3)  It  is  probable  that  the  presence  of  free  acid  in  solvents  other  than 
water  will  lead  to  the  discovery  of  many  new  bands  of  neodymium,  erbium, 
etc.    A  striking  example  of  this  kind  is  the  effect  of  dissolving  hydrochloric 
acid  gas  in  a  neodymium  chloride  solution  in  ethyl  alcohol.    The  effect  of  the 
free  acid  is  to  bring  out  very  strongly  bands  at  X  3695  and  X  3760.    The  pres- 
ence of  sodium  perchlorate  has  a  similar  effect. 

(4)  Mixtures  of  varying  amounts  of  two  salts  in  the  same  solvent  may 
result  in  a  gradual  shift  from  the  bands  of  one  salt  into  the  bands  of  the  other, 
the  shift  depending  on  the  amount  of  each  salt  present.    As  an  example  of  this, 
uranyl  sulphate  and  uranyl  nitrate  were  studied.    On  the  other  hand,  there 
are  examples  where  the  two  salts  do  not  seem  to  form  any  intermediate  aggre- 
gates, and  the  bands  of  each  simply  vary  in  intensity  without  showing  any 
change  in  frequency. 

(5)  Acid  aggregates  of  uranous  salts  are  found  to  be  much  more  stable 
than  the  neutral  aggregates.    Uranous  nitrate,  for  instance,  is  very  unstable; 
but  uranous  chloride  dissolved  in  concentrated  nitric  acid  (the  absorption 
spectrum  is  entirely  different  from  that  of  uranous  chloride)  will  stand  for  hours 


SUMMARY    AND    GENERAL    DISCUSSION    OF    RESULTS.  97 

before  it  is  oxidized  to  the  uranyl  condition.  Neutral  uranous  salts  in  solu- 
tion, when  heated  to  80°  or  90°,  form  a  black  precipitate;  but  if  some  free 
acid  is  present  (or  in  the  case  of  uranous  chloride  if  other  chlorides  are  present) 
the  uranous  salts  are  much  more  stable. 

(6)  Aggregates  form  compounds  with  solvents  in  many  cases  (for  example, 
various  uranous  aggregates  in  water  and  methyl  alcohol)  that  are  as  charac- 
teristic as  those  formed  by  the  pure  neutral  salt.    As  yet  no  work  has  been 
done  on  the  effect  of  temperature  and  concentration  on  solvate  aggregates. 

(7)  In  discussing  the  differences  in  the  chemical  properties  of  aggregates 
mention  will  be  made  of  the  reduction  and  oxidization  of  uranium  salts.    It 
is  probable  that  many  other  chemical  properties  differ  very  much  for  the 
various  aggregates,  but  as  this  work  has  been  mainly  concerned  with  the 
reduction  and  the  oxidization  of  the  salts,  only  these  properties  will  be  con- 
sidered.   As  some  of  the  methods  used  in  the  reduction  of  the  uranyl  salts 
are  in  themselves  of  considerable  interest,  they  will  be  taken  up  in  more 
detail  than  would  otherwise  be  done. 

The  method  employed  for  the  preparation  of  the  uranous  salts  for  work 
on  absorption  spectra  has  been  that  described  by  Jones  and  Strong.1  Under 
these  conditions  it  is  possible  to  obtain  quite  concentrated  solutions  of  the 
chloride,  the  bromide,  and  the  sulphate.  No  aqueous  solution  of  uranous 
nitrate  could  be  obtained,  although  small  amounts  would  be  formed  when  the 
hydrogen  was  first  liberated  from  the  acid,  but  in  a  very  short  time  the  uranous 
nitrate  was  oxidized. 

The  most  concentrated  solution  of  any  uranous  salt  thus  far  obtained 
is  that  of  the  chloride.  Uranyl  chloride  is  dissolved  in  ether  (the  solution 
forms  three  distinct,  unmiscible  layers,  the  concentration  of  uranyl  chloride 
in  each  being  different).  To  this  solution  is  added  a  small  amount  of  zinc 
and  concentrated  hydrochloric  acid.  The  uranous  chloride  formed  is  insoluble 
in  ether  and  accumulates  in  the  dark  oily  liquid  at  the  bottom  of  the  vessel. 
Layers  of  this  liquid  1  mm.  thick  are  almost  opaque.  The  reduction  of 
uranyl  chloride  in  isobutyl  alcohol  is  very  similar  to  that  in  ether. 

When  hydrochloric  acid  and  zinc  are  added  to  a  solution  of  uranyl  nitrate 
a  considerable  amount  of  a  uranous  salt  is  formed,  although  it  is  quickly 
oxidized  again.  This  is  true  even  when  quite  large  amounts  of  hydrochloric 
acid  are  present.  A  much  more  complete  spectrographic  study  of  the  reduc- 
tion of  uranyl  aggregates  should  be  made,  as  it  would  probably  lead  to  some 
knowledge  as  to  how  the  oxygen  atoms  are  removed  from  the  uranyl  group 
and  the  influence  the  other  atoms  and  molecules  of  the  aggregate  have  upon 
this  reduction. 

(8)  Oxidization  reactions  also  indicate  very  clearly  that  different  aggre- 
gates apparently  possess  different  properties,  although  the  action  of  the  other 
salts  or  acids  present  in  the  solution  may  modify  the  action  of  the  oxidizing 
agent.    However  this  may  be,  it  is  found  that  uranous  acid  aggregates  require 
a  great  deal  more  of  the  oxidizing  agent,  especially  when  this  is  hydrogen 
peroxide,  than  do  the  neutral  aggregates. 

(9)  Assuming  the  presence  of  aggregates,  it  is  important  to  know  what 
effect  dilution  has  upon  their  composition.    It  would  be  supposed  that  the 
aggregates  would  break  down  at  high  dilution.    To  test  this  supposition  the 

1  Phil.  Mag.,  19,  566  (1910) 


98  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

absorption  spectra  of  uranyl  nitrate  and  uranyl  sulphate  were  photographed 
at  very  great  dilution.  If  dissociation  is  sufficiently  complete  it  would  be 
expected  that  the  uranyl  nitrate  bands  would  shift  towards  the  red  with 
decrease  in  concentration,  and  the  uranyl  sulphate  bands  would  shift  towards 
the  violet,  so  that  for  very  great  dilution  the  uranyl  bands  of  both  salts  would 
be  identical.  This  was  not  found  to  be  the  case.  There  appeared  a  very 
slight  shift  of  the  uranyl  nitrate  bands  to  the  red,  and  possibly  a  slight  shift 
of  the  uranyl  sulphate  bands  to  the  violet;  but  these  shifts  were  extremely 
small;  so  small,  indeed,  that  some  observers  who  looked  at  the  spectrograms 
did  not  detect  it  at  all.  If  the  shifts  occur,  it  is  exactly  what  would  be  expected 
if  the  uranyl  nitrate  and  uranyl  sulphate  aggregates  break  up  into  complex 
ions.  The  loss  of  an  NO.-,  group  would  cause  the  uranyl  nitrate  bands  to  shift 
only  slightly  to  the  red  if  the  aggregate  was  of  some  size,  and  the  same  would 
be  true  of  the  uranyl  sulphate  aggregate.  If  this  theory  is  true  it  indicates 
that  the  aggregates  possess  quite  a  high  degree  of  complexity. 

(10)  The  question  has  been  asked  as  to  whether  the  aggregates  are  definite 
chemical  compounds,  whether  they  have  a  definite  composition,  and  how 
stable  they  are.  Unfortunately  the  spectroscopic  method  itself  can  not  solve 
these  problems,  but  by  studying  the  composition  of  the  acid  aggregate  precipi- 
tates that  are  often  formed,  and  the  chemical  composition  and  absorption 
spectra  of  these,  much  light  may  be  thrown  on  the  subject.  The  other  physical 
and  chemical  properties  of  solutions  containing  aggregates  should  also  be 
studied. 

THE    EFFECT    OF    TEMPERATURE    ON    ABSORPTION    SPECTRA. 

(1)  The  general  effect  of  rise  in  temperature  is  to  give  a  solution  of  an 
inorganic  salt  a  deeper  color.    This  deepening  of  the  color  signifies  that  the 
absorption  of  light  has  become  more  selective,  and  spectroscopic  work  indi- 
cates that  this  selective  absorption  is  usually  due  to  a  widening  of  the  absorp- 
tion bands.    As  these  bands  are  never  so  distributed  over  the  spectrum  as  to 
give  a  colorless  solution,  it  follows  that  a  widening  of  the  absorption  bands  will 
intensify  the  color  of  the  solution.    In  many  cases  this  widening  appears  to 
be  quite  unsymmetrical,  but  this  need  not  necessarily  mean  that  the  center  of 
gravity  of  the  individual  absorption  band  is  shifted.    Many  examples  of  the 
neodymium  absorption  bands  show  this  phenomenon  very  clearly.     For 
instance,  the  absorption  due  to  the  7  and  5  groups  of  bands  may  be  sufficiently 
intense  to  make  these  groups  appear  as  single  bands.    If  the  absorption  is 
not  so  intense  as  this,  in  some  solvents  it  is  found  that  with  rise  in  temperature 
the  shortest  wave-length  bands  may  decrease  in  intensity,  and  may  even  dis- 
appear.   The  long  wave-length  bands  increase  in  intensity,  and  in  some  cases 
new  bands  appear.    Knowing  this,  it  is  easy  to  understand  that  if  the  absorp- 
tion is  so  strong  that  each  of  these  groups  of  bands  appears  as  a  single  band, 
these  broad  bands  will  widen  very  unsymmetrically  towards  the  red  with  rise 
in  temperature.    It  may  be  that  some  change  like  this  takes  place  in  the  case 
of  the  uranyl  bands.    It  is  for  this  reason  that  a  formula  calculated  for  the  widen- 
ing of  a  band  with  rise  in  temperature  would  not  apply  to  many  wide  bands. 

(2)  In  the  case  of  all  pure  salts  dissolved  in  a  single  solvent,  the  bands 
have  been  found  to  widen  with  rise  in  temperature,  and  at  the  same  time  the 


SUMMARY    AND    GENERAL    DISCUSSION    OF    RESULTS.  99 

bands  become  more  diffuse,  the  edges  becoming  hazier.  When  there  is  a 
mixture  of  salts  in  the  same  solvent,  the  bands  may  become  much  weaker 
with  rise  in  temperature.  This  is  the  case  in  a  mixture  of  neodymium  and 
calcium  chlorides  in  water.  In  a  similar  manner  the  absorption  of  a  salt  in 
two  solvents  probably  decreases  in  intensity  with  rise  in  temperature.  An 
example  of  this  kind  is  that  of  uranous  bromide  in  40  per  cent  water  and  60 
per  cent  alcohol.  At  ordinary  temperatures  the  bands  are  of  about  equal 
intensity.  At  80°  the  water-bands  have  practically  disappeared,  without  the 
alcohol  bands  having  widened  to  any  great  extent. 

(3)  In  general  the  center  of  intensity  of  single  bands  changes  but  little. 
Whenever  there  is  any  change  of  wave-length,  the  shift  is  invariably  towards 
the  red.    It  seems  that  this  shift  is  greater  the  wider  the  band,  so  that  it  is 
difficult  to  say  in  most  cases  whether  the  shift  is  real  or  only  apparent.    In 
the  case  of  solutions  of  pure  neodymium  and  erbium  salts  the  shift  is,  in  general, 
too  small  to  be  observed. 

(4)  A  study  of  gaseous  aggregates  such  as  N2O4  ^  2NOa  indicates  that 
raising  the  temperature  or  lowering  the  pressure  increases  the  relative  number 
of  the  simpler  molecules.     Many  vapors  like  those  of  the  fatty  acids  show 
molecular  clustering  at  low  temperatures.    In  a  similar  manner  it  would  be 
expected  that  aggregates  would  gradually  break  down  at  the  higher  tempera- 
tures.   In  considering  specific  examples,  it  would  be  expected  that  acid  uranyl 
sulphate  aggregates  in  breaking  down  would  result  in  a  shift  of  the  uranyl 
bands,  the  shift  being  towards  the  violet.    On  the  other  hand,  if  the  nitric 
acid  uranyl  nitrate  aggregates  are  broken  down,  it  would  be  expected  that 
the  uranyl  bands  would  be  shifted  towards  the  red.    According  to  this  view 
the  shift  of  the  uranyl  bands  of  uranyl  nitrate  in  nitric  acid  and  of  uranyl 
sulphate  in  sulphuric  acid,  with  rise  in  temperature,  should  be  quite  different 
if  the  only  effect  of  rise  in  temperature  is  a  breaking  up  of  the  aggregates. 

In  advancing  an  hypothesis  of  this  kind  it  is  assumed  that  it  is  only  the 
molecules  in  an  aggregate  that  are  effective  in  changing  the  frequency  of 
vibration  of  the  absorbing  systems  of  the  light  centers.  This  means  that  the 
kinetic  energy  of  the  aggregate  corresponds  to  that  of  a  molecule  at  the  same 
temperature  in  the  solution,  the  individual  molecules  in  an  aggregate  all 
moving  together.  Whether  there  is  a  constant  interchange  of  these  molecules 
and  the  molecules  of  the  solution,  spectroscopic  evidence  does  not  as  yet  show. 
Neither  can  it  be  said  with  certainty  that  molecules  outside  the  aggregates 
do  not  affect  the  frequencies  of  vibration  of  the  absorbing  system  within  the 
aggregate.  Assuming  that  this  is  not  the  case,  then  it  follows  of  necessity 
that  with  rise  in  temperature  the  acid  aggregates  are  not  broken  up,  because 
the  uranyl  bands  of  acid  solutions  are  then  shifted  to  the  red.  This  shift 
seems  to  be  about  as  great  for  uranyl  sulphate  in  sulphuric  acid  as  it  is  for 
uranyl  nitrate  in  nitric  acid.  In  a  similar  manner,  acid  solutions  of  neodym- 
ium salts  do  not  have  their  absorption  spectra  changed  so  as  to  resemble  more 
closely  that  of  the  neutral  salt,  with  rise  in  temperature,  as  one  would  expect 
if  the  acid  neodymium  aggregates  were  broken  down. 

(5)  When  foreign  salts  like  calcium  chloride  are  added  to  solutions  of 
neodymium  chloride,  it  is  probable  that  aggregates  containing  the  two  salts 
are  formed.    In  the  case  of  aqueous  solutions  of  these  salts  it  is  found  that 


100  THE    ABSORPTION    SPECTRA    OF    SOLUTIONS. 

the  neodymium  bands  are  shifted  to  the  red  with  rise  in  temperature,  whereas 
aqueous  solutions  of  pure  neodymium  chloride  do  not  show  this  effect  at  all. 
Exactly  what  takes  place  in  this  case  is  not  evident. 

(6)  The  effect  of  rise  in  temperature  on  solutions  showing  the  solvate 
bands  of  equal  intensity  has  been  to  cause  a  change  in  the  intensity  of  the 
solvate  bands;  very  little  if  any  change,  however,  in  the  wave-lengths  of  the 
bands  takes  place.    In  the  case  of  water  and  alcohol,  the  alcohol  bands  increase 
in  persistency  as  the  temperature  is  raised. 

(7)  In  the  work  with  the  closed  cell  at  high  temperatures  it  was  found 
that  precipitates  were  formed  in  practically  every  case,  probably  due  to  hy- 
drolysis, alcoholysis,  etc.,  precipitation  taking  place  in  dilute  as  well  as  in  con- 
centrated solutions.     Several  examples  were  tested  of  concentrated  solutions 
of  colored  salts  mixed  with  calcium  or  aluminium  chloride,  and  precipitation 
was  found  to  take  place  under  these  conditions  at  comparatively  low  tem- 
peratures.   It  would  be  very  interesting  to  learn  whether  acid  aggregates  of 
uranyl,  neodymium,  erbium  and  such  salts  are  less  likely  to  form  precipi- 
tates than  the  neutral  salt  solutions. 

In  the  case  of  neutral  uranous  solutions  these  precipitates  form  at  70° 
or  80°.  The  presence  of  acid  prevents  this  precipitation  at  temperatures 
below  100°. 

Whether  the  salt  precipitation  at  high  temperatures  is  complete  or  not, 
can  not  be  decided  in  general  at  present.  In  the  case  of  several  neodymium 
and  erbium  solutions  this  seemed  to  be  the  case.  In  one  of  the  uranyl  solu- 
tions, however,  some  uranyl  salt  remained  in  the  solution  after  the  precipitate 
had  settled. 

(8)  It  may  be  said,  in  general,  that  there  is  a  very  great  increase  in  the 
absorption  of  all  solutions  in  the  short  wave-length  region  of  the  spectrum 
as  the  temperature  is  raised.    How  great  this  increase  in  absorption  would 
be  if  pure  solutions  were  used  has  not  yet  been  determined.    The  formation 
of  precipitates  is  usually  preceded  by  a  very  great  increase  in  the  short  wave- 
length absorption. 

(9)  The  problem  as  to  whether  a  rise  in  temperature  produces  a  perma- 
nent change  in  the  structure  of  the  aggregates  in  solution  has  not  been  studied 
to  any  great  extent.    In  the  case  of  the  existence  of  two  solvent  spectra  it  is 
found  that  the  spectra  on  cooling  the  solution  are  exactly  the  same  as  before 
heating.    In  the  case  of  an  acetone  solution  of  uranyl  chloride  it  was  found 
that  the  bands  are  apparently  single  after  the  precipitate  was  formed  during 
the  heating.    Whether  these  bands  would  have  become  double  again  when  the 
solution  was  cooled  was  not  tested.    It  would  be  interesting  to  learn  whether 
selective  solvate  precipitation  would  take  place  on  heating  solutions. 

(10)  It  seems  worth  while  in  conclusion  to  call  attention  to  the  promising 
and  important  application  of  spectrophotography  at  low  temperatures  to 
the  study  of  the  nature  of  chemical  reactions.    As  soon  as  the  changes  in 
breadth,  intensity,  and  frequency  of  individual  absorption  bands  and  the 
constitution  of  the  groups  of  bands  can  be  interpreted,  our  knowledge  of  the 
relation  between  absorption  centers  or  aggregates  and  the  other  physical  and 
chemical  units  of  matter  will  be  much  more  fully  understood;  and  the  changes 
which  these  particles  undergo  will  be  much  better  comprehended. 


DESCRIPTION  OF  PLATES. 

With  the  exception  of  the  plates  representing  changes  in  temperature  of  the  solution, 
the  times  of  exposure  and  the  width  of  the  slit  are  the  same  for  each  strip  of  the  plate.  The 
current  through  the  Nernst  glower  was  kept  constant.  In  the  case  of  the  uranyl  salts  a 
much  longer  exposure  is  often  made  in  the  ultra-violet  and  violet,  in  order  to  bring  out  the 
uranyl  bands  as  strongly  as  possible,  and  this  will  be  noted  in  the  description.  In  some 
strips  ultra-violet  wave-length  spark  lines  will  be  found,  these  being  photographed  without 
the  solution  in  the  path  of  the  light,  and  only  for  purposes  of  measurement.  In  exposures 
to  the  spark  of  this  kind,  the  film  holder  was  never  moved  between  the  photographing 
of  the  absorption  spectra  of  the  solution  and  that  of  the  spark  spectra.  In  some  instances 
the  strips  are  not  uniformly  exposed.  This  was  due  in  many  cases  to  the  formation  of 
precipitates.  A  great  deal  of  trouble  of  this  kind  was  encountered,  especially  with  the 
uranous  salts,  in  the  high  temperature  work,  and  in  the  spectrophotography  of  chemical 
reactions.  In  referring  to  the  strips,  the  first  or  lowest  strip  will  be  that  at  the  bottom  of 
the  plate — the  one  that  is  nearest  the  scale  of  wave-lengths.  The  scale  of  wave-lengths 
is  in  Angstrom  units,  the  whole  number  standing  for  so  many  hundred  Angstrom  units. 

PLATE  1.  A.  Lithium  Chromate  in  Water.  Depths  of  cell  and  concentrations,  starting 
with  the  lowest  strip:  0.25  normal,  3mm.;  0.25  normal,  24  mm.;  0.46  nor- 
mal, 24  mm.;  1.0  normal,  24  mm.;  1.5  normal,  24  mm.;  and  2.0  normal 
24  mm. 

B.  Lithium  Bichromate  in  Water.  Depths  of  cell  and  concentrations,  start- 
ing with  the  lowest  strip:  0.25  normal,  3  mm.;  0.25  normal,  24  mm.;  0.46 
normal,  24  mm.;  1.0  normal,  24  mm.;  and  2.0  normal,  24  mm. 

PLATE  2.  A.  Calcium  Ferricyanide  in  Water.  Depth  of  cell  kept  constant,  24  mm.  Con- 
centrations, starting  with  the  lowest  strip,  0.031,  0.058,  0.125,  0.175, 
and  0.25  normal. 

B.  Calcium  Ferrocyanide  in  Water.  Depth  of  cell  kept  constant,  24  mm.  Con- 
centrations, starting  with  the  lowest  strip,  0.25,  0.46,  0.66,  1.0,  1.5,  and 
2.0  normal. 

PLATE     3.  A.  Aluminium  Chromate  in  Water.    Depths  of  cell,  3,  24,  24.  and  24  mm.  Con- 
centration could  not  be  determined  on  account  of  hydrolysis. 
B.  Calcium  Chromate  in  Water.    Depth  of  cell  constant,  24  mm.    Concentra- 
tion somewhat  less  than  0.01  normal. 

PLATE  4.  A.  Copper  Bichromate  in  Water.  Depths  of  cell  and  concentrations,  starting 
with  the  lowest  strip:  3  mm.,  0.044  normal;  24  mm.,  0.044  normal;  24  mm., 
0.08  normal;  24  mm.,  0.117  normal;  24  mm.,  0.175  normal;  24  mm.,  0.26 
normal;  and  24  mm.,  0.35  normal. 

B.  Potassium  Nickel  Chromate  in  Water.  The  depth  of  cell  was  kept  constant 
at  24  mm.,  and  the  concentration  could  not  be  determined  on  account  of 
hydrolysis. 

PLATE  5.  A.  Neodymium  Chloride  in  Butyl  Alcohol.  Depth  of  cell  10  cm.  and  concen- 
tration 0.024  normal,  strip  1,  and  in  Butyl  Alcohol,  depth  of  cell  3  cm. 
and  concentration  0.04  normal,  strip  2. 

B.  Neodymium  Chloride  in  Glycerol  and  Ethyl  Alcohol,  concentration  con- 
stant, 0.5  normal.     Depth  of  cell  constant,  18  mm.;  starting  with  the 
lowest  strip  the  following  numbers  represent  the  percentage  of  the  solvents : 
10,     15,     20,     40,     60    glycerol. 
90,     85,     80,     60,     40     ethyl  alcohol. 

PLATE  6.  A.  Neodymium  Chloride  in  Isopropyl  Alcohol.  Depth  of  cell  30  mm.  Con- 
centration, 0.0266  normal. 

B.  Neodymium  Nitrate  in  Tertiary  Butyl  Alcohol.    Concentration,  0.2  normal. 

C.  Neodymium  Chloride  in  Water  and  Alcohol.     The  lower  strip  represents 

about  8  per  cent  water  and  shows  both  sets  of  bands.    Concentration, 
0.5  normal.    The  other  strips  show  the  effect  of  adding  hydrogen  peroxide. 

101 


102  DESCRIPTION    OF    PLATES. 

PLATE     7.  A.  Neodymium  Chloride  in  Propyl  Alcohol.  Depth  of  cell  constant, 30  mm.  Con- 
centrations, starting  with  lowest  strip,  0.04,  0.03,  0.02,  and  0.0133  normal. 
B.  Neodymium  Nitrate  in  Propyl  Alcohol.     Depth  of  cell  constant,  16  mm. 
Concentrations,  starting  with  lowest  strip,  0.05,  0.07,  0.10,  0.15,  0.225, 
and  0.3  normal. 

PLATE  8.  A.  Neodymium  Chloride  in  Isobutyl  Alcohol.  Depth  of  cell  constant,  34  mm. 
Concentrations,  starting  with  lowest  strip,  0.024,  0.018,  0.012,  and  0.008 
normal. 

B.  Neodymium  Nitrate  in  Isobutyl  Alcohol.  Depth  of  cell,  16  mm.  Concen- 
trations, starting  with  lowest  layer,  0.05,  0.07,  0.10,  0.15,  0.225,  and  0.3 
normal. 

PLATE  9.  A.  Neodymium  Nitrate  in  Butyl  and  Isobutyl  Alcohols.  Strip  1  is  a  3  mm. 
and  strip  2  a  13  mm.  layer  of  a  0.3  normal  solution  in  butyl  alcohol; 
strip  3  is  a  3  mm.  and  strip  4  a  13  mm.  layer  of  a  0.6  normal  solution  in 
isopropyl  alcohol. 

B.  Neodymium  Nitrate  in  mixtures  of  Ethyl  and  Isobutyl  Alcohols.    Depth  of 
cell  constant,  34  mm.     Concentration  constant,  0.1  normal.     Starting 
with  lowest  strip  the  percentages  of  the  solvents  were: 
20,     40,     60,     80,     100    ethyl  alcohol. 
80,     60,     40,     20,        0    isobutyl  alcohol. 

PLATE  10.  A.  Neodymium  Nitrate  in  Methyl  Ester.  Depth  of  cell  constant,  18  mm. 
Concentrations,  starting  with  lowest  strip,  0.05,  0.07,  0.10,  0.15,  0.225, 
and  0.3  normal. 

B.  Neodymium  Nitrate  in  Ethyl  Ester.  Depth  of  cell  constant,  18  mm.  Con- 
centrations, starting  with  lowest  strip,  0.05,  0.07,  0.10,  0.15,  0.225,  and 
0.3  normal. 

PLATE  11.  A.  Neodymium  Nitrate  in  Anthracene  and  Ethyl  Acetate.  The  variable  quantity 
here  is  depth  of  cell.  The  early  investigators  made  experiments  to  test 
whether  two  colored  salts  in  the  same  solvent  having  bands  that  were  of 
almost  the  same  wave-lengths  had  the  wave-lengths  of  these  bands  changed 
with  reference  to  the  wave-lengths  of  the  bands  for  the  solutions  of  the 
separate  salts.  At  present  this  would  hardly  be  expected  to  result,  unless 
double  solvates  were  formed,  i.e.,  compounds  containing  the  two  salts 
and  the  solvent.  This  spectrogram  was  taken  to  find  whether  the 
anthracene  and  neodymium  bands  had  their  wave-lengths  affected  by 
both  being  dissolved  in  ethyl  ester.  This  might  be  expected  if  compounds 
were  formed  containing  both  anthracene  and  neodymium  nitrate.  The 
bands  are  in  the  ultra-violet.  Unfortunately  it  is  very  difficult  to  obtain 
the  anthracene  and  neodymium  bands  together. 

B.  Neodymium  Nitrate  in  Ethyl  Acetate  and  Anthracene.  To  obtain  this 
spectrogram  it  was  necessary  to  heat  the  solutions  in  order  to  keep  the 
anthracene  in  solution.  The  percentages  of  anthracene  for  the  6  strips, 
starting  with  the  lowest,  were:  0.25,  0.5,  0.75,  1,  1.5,  and  2. 

PLATE  12.  A.  Neodymium  Nitrate  in  Ethyl  Acetate  and  Anthracene.    Concentration  of 
neodymium  nitrate,  0.24  normal.     Succeeding  strips  show  the  effect  of 
adding  ethyl  alcohol,  methyl  alcohol  and  acetic  acid,  respectively. 
B.  Neodymium  Nitrate  in  Ethyl  Acetate  and  Anthracene.    The  lowest  strip 
is  the  only  one  that  shows  the  anthracene  bands. 

PLATE  13.  A.  Neodymium  Acetate  in  Formamide.  The  acetate  slowly  decomposes,  form- 
ing a  white  precipitate.  Strips  1  and  2  represent  different  depths  of  cell 
(strip  2  being  35  mm.).  Strip  3  is  the  same  as  2  after  water  has  been 
added.  The  original  film  shows  quite  a  large  shift  of  the  neodymium 
bands  towards  the  violet  in  the  upper  strip,  compared  with  the  second  strip. 
B.  Uranyl  and  Uranous  Sulphates  in  Water,  to  which  Acetic  Acid  is  added . 
Starting  with  strip  1  increasing  amounts  of  acetic  acid  are  added  to  an 
aqueous  solution  of  uranyl  sulphate.  This  results  in  a  precipitate  (strip 
5),  and  the  solution  is  filtered  and  the  absorption  spectra  again  taken 
(strip  6).  Strips  7  and  8  represent  the  uranous  salt  formed  from  the  solu- 
tion used  for  strip  6  when  zinc  is  added. 


DESCRIPTION    OF    PLATES.  103 

PLATE  14.  A.  Uranyl  Chloride  in  Isopropyl  Alcohol.     Concentration  of   the  chloride, 

0.005  normal.    Depth  of  cell  variable. 

B.  Uranyl  Chloride  in  Ethyl  Acetate.  Depths  of  cell,  starting  with  lowest 
strip,  12,  24,  24,  24,  24,  24,  24,  and  24  mm.  Concentrations,  0.075, 
0.075,  0.01,  0.014,  0.02,  0.03,  0.045,  and  0.06  normal. 

PLATE  15.  A.  Strip  1  is  the  absorption  of  a  solution  35  mm.  deep  of  Uranyl  Nitrate  in 
Methyl  Ester.  Strip  2  is  the  absorption  of  Erbium  Chloride  (35  mm.) 
in  Propyl  Alcohol.  The  other  strips  represent  the  absorption  of  Uranyl 
Chloride  in  Butyl  Alcohol. 

B.  Uranyl  Chloride  in  Formamide.  Depths  of  cell,  3,  15,  15,  15, 15,  and  15  m. 
Respective  concentrations,  0.073, 0.073, 0.1, 0.147, 0.219,  and  0.293  normal. 

PLATE  16.  A.  Uranyl  Chloride  in  Water,  to  which  increasing  amounts  of  an  aqueous  solu- 
tion of  Calcium  Nitrate  are  added.  This  spectrogram  was  made  to  deter- 
mine whether  the  addition  of  calcium  nitrate  resulted  in  a  gradual  shift 
of  the  uranyl  bands.  The  original  film  shows  that  the  A  and  B  bands 
decrease  in  intensity,  and  the  decrease  seems  to  be  considerably  greater 
on  the  red  side  of  the  bands. 

B.  Uranyl  Nitrate  in  Nitric  Acid,  to  which  increasing  amounts  of  a  concen- 
trated aqueous  solution  of  Aluminium  Chloride  are  added.  The  first  addi- 
tion consisted  of  three  drops,  and  shows  a  large  shift  of  the  uranyl  bands 
towards  the  red.  A  gradual  shift  towards  the  red  is  shown  by  the  suc- 
ceeding strips  in  the  original  film. 

PLATE  17.  A.  Uranyl  Nitrate  in  Nitric  Acid  to  which  increasing  amounts  of  Hydrochlo- 
ric Acid  are  added. 

B.  Uranyl  Nitrate  in  Water  to  which  an  aqueous  solution  of  Aluminium 
Chloride  is  added.  This  spectrogram  shows  very  clearly  the  shift  of  the 
uranyl  bands  towards  the  red. 

PLATE  18.  A.  Uranous  Chloride  in  Propyl  Alcohol.    The  variable  here  is  the  depth  of  cell. 
B.  Uranyl  Chloride  in  Propyl  Alcohol.     Depths  of  cell,  3,  12,  24,  24,  24,  24. 
and  24  mm.     Respective  concentrations,  0.025,  0.025,  0.033,  0.046,  0.06, 
0.1,  0.15,  and  0.2  normal. 

PLATE  19.  A.  Uranous  Chloride  in  Isobutyl  Alcohol. 

B.  Uranyl  Chloride  in  Isobutyl  Alcohol.  Starting  with  strip  1  the  depth  of 
cell  was  10  mm.;  succeeding  depths  were  24  mm.  The  corresponding 
concentrations  were:  0.02,  0.027,  0.037,  0.053,  0.08,  0.12,  and  0.16  normal. 

PLATE  20.  A.  Uranous  Chloride  in  Isobutyl  Alcohol.  When  uranyl  chloride  in  isobutyl 
alcohol  is  reduced  by  the  addition  of  zinc  and  a  small  amount  of  con- 
centrated hydrochloric  acid,  the  uranous  chloride  formed  appears  as  dark 
green,  oily  looking  drops,  which  collected  at  the  bottom  of  the  solution. 
The  remainder  of  the  solution  dissolves  only  a  very  small  portion  of  the 
uranous  chloride.  19  A  represents  the  absorption  of  the  dilute  portion; 
whereas  this  plate  represents  the  absorption  of  very  thin  layers  of  the 
concentrated  solution  of  uranous  chloride. 

B.  Uranyl  Chloride  hi  Methyl  Ester.  Starting  with  strip  1  the  depths  of  cell  and 
concentration  were:  10  mm.,  0.021;  24  mm.,  0.028;  24  mm.,  0.04;  24  mm., 
0.057;  24  mm.,  0.085;  24  mm.,  0.13;  and  24  mm.,  0.17  normal. 

PLATE  21.  A.  Uranous  Chloride  in  Propyl  Alcohol. 

B.  Uranyl  Nitrate  in  Propyl  Alcohol.  Strip  1  has  a  depth  of  cell  of  10  mm. 
and  the  depth  for  the  other  strips  is  24  mm.  The  concentrations  were 
0.08,  0.10,  0.15,  0.21,  0.32,  0.48,  and  0.63  normal. 

PLATE  22.  A.  Uranyl  Nitrate  in  Water  to  which  increasing  amounts  of  Calcium  Nitrate 
were  added.  The  addition  of  calcium  chloride  would  cause  the  uranyl 
bands  to  be  shifted  towards  the  red.  If  this  is  due  to  the  presence  of 
calcium,  then  calcium  nitrate  should  also  cause  the  uranyl  bands  to 
shift  towards  the  red.  This  does  not  appear  from  the  plate,  the  bands 
being  practically  of  the  same  wave-lengths  after  calcium  nitrate  had 
been  added.  This  spectrogram  (the  film  at  least)  gives  evidence  that  the 
effective  agent  in  causing  the  shifts  of  the  uranyl  bands  is  the  acid  radicle. 
B.  Uranous  Chloride  in  Ether  and  Hydrochloric  Acid  to  which  Acetone  is  added. 


104  DESCRIPTION    OF    PLATES. 

PLATE  23.  A.  Uranous  Bromide  in  Water  to  which  Methyl  Alcohol  is  added.  This  spec- 
trogram shows  the  great  difference  between  the  water  and  methyl  alco- 
hol bands  of  uranous  bromide. 

B.  Uranous  Chloride  in  Water  to  which  Methyl  Alcohol  is  added.    The  methyl 
alcohol  was  added  in  smaller  quantities  than   to  the  solutions  whose 
spectrograms  are  recorded  in  the  above  plate. 
PLATE  24.  A.  Uranous  Chloride  in  Methyl  Ester  to  which  Water  is  added. 

B.  Uranous  Chloride  in  Methyl  Ester.    Depth  of  cell  is  gradually  increased. 
PLATE  25.  A.  Uranous  Chloride  in  Ethyl  Ester.    Depth  of  cell  variable. 

B.  Uranous  Acetate  in  Acetone.    Depth  of  cell  variable. 
PLATE  26.  A.  Uranous  Chloride  in  Ether.    Depth  of  cell  variable. 

B.  Uranous  Chloride  in  Acetone.    Depth  of  cell  variable. 

PLATE  27.  A.  Uranous  Chloride  in  concentrated  Nitric  Acid.  The  uranous  chloride  is 
added  to  the  acid  which  was  placed  in  the  Uhler  cell.  It  is  very  remark- 
able that  the  uranous  salt  is  not  oxidized  under  these  conditions. 

B.  Uranous  Bromide  in  Water  and  Methyl  Alcohol  after  the  precipitate  has 

been  filtered  off  (strip  1).  This  shows  a  selective  precipitation  of  the 
hydrate.  The  succeeding  strips  show  the  absorption  of  uranous  bromide 
in  water  and  methyl  alcohol  to  which  increasing  amounts  of  nitric  acid 
(in  the  same  proportion  of  water  and  alcohol)  are  added. 

C.  Uranous  Chloride  in  Propyl  Alcohol  to  which  Acetone  is  gradually  added. 
PLATE  28.  A.  Gadolinium  Chloride  in  Ethyl  Alcohol.    Concentration  constant,  0.8  normal. 

Depths  of  cell,  starting  with  the  lowest  strip,  2,  4,  9,  18,  27,  and  27  mm. 
In  the  upper  strip  an  exposure  was  made  directly  to  the  ultra-violet  spark 
lines. 

B.  Gadolinium  Chloride  in  Water.  Concentration  constant,  1.407  normal. 
Depths  of  cell,  starting  with  the  lowest  strip,  2,  10,  15,  22,  22,  and  100  mm. 
In  the  upper  two  strips  an  exposure  was  made  directly  to  the  ultra-violet 
spark  lines. 

PLATE  29.  A.  Dysprosium  Chloride  in  Methyl  Alcohol.  Concentration  about  normal.  In 
all  the  spectrograms  of  gadolinium,  dysprosium,  and  samarium,  the  slit 
width  was  0.10  mm.,  the  current  in  the  Nernst  glower  0.9  ampere,  and 
the  length  of  exposure  was  1  minute  to  the  visible  portion  of  the  Nernst 
glower  spectrum,  and  about  5  minutes  to  the  ultra-violet  part  of  the 
Nernst  glower  spectrum.  The  depths  of  cell  were  1,  5,  12,  20,  31,  and 
31  mm.  The  upper  strip  was  exposed  directly  to  the  ultra-violet  spark  lines. 

B.  Dysprosium  Chloride  in  Water.  Concentration,  1.86  normal.  Depths  of 
cell,  starting  with  lowest  strip,  2,  6,  10,  15,  21,  and  100  mm.  All  the 
strips  except  the  lowest  one  were  exposed  directly  to  the  ultra-violet  spark 
lines. 

PLATE  30.  A.  Dysprosium  Chloride  in  Water.  Concentration,  1.86  normal.  Depths  of 
cell,  starting  with  lowest  strip,  2,  8,  16,  and  21  mm. 

B.  Dysprosium  Acetate  in  Water  to  which  varying  amounts  of  Nitric  Acid 
were  added.  Concentration  of  the  neutral  solution,  0.4  normal.  The  in- 
creased depth  of  cell  is  due  to  the  addition  of  concentrated  nitric  acid. 
Starting  with  the  lowest  strip  the  depths  of  cell  were:  15,  15.1,  15.3,  15.7, 
16.7,  and  32  mm. 

PLATE  31.  A.  Dysprosium  Acetate  in  Water.  Concentration,  0.4  normal.  Depths  of  cell, 
starting  with  lowest  strip,  4,  16,  25,  and  34  mm.  Exposures  were  made 
in  strips  2,  3,  5  directly  to  the  ultra-violet  spark  lines. 

B.  Dysprosium  Chloride  hi  Ethyl  Alcohol.  Concentration,  0.74  normal.  Depths 
of  cell,  2, 10, 15,  24,  30,  and  30  mm.  The  upper  strip  was  exposed  directly 
to  the  ultra-violet  spark  lines. 

PLATE  32.  A.  Samarium  Chloride  in  Water.  Concentration,  1.31  normal.  Depths  of 
cell,  starting  with  lowest  strip,  2,  6,  12,  16,  20,  and  100  mm.  Strips  3,  4, 
5,  6  were  exposed  directly  to  the  ultra-violet  spark  lines. 

B.  Samarium  Chloride  in  Methyl  Alcohol.  Concentration  about  normal. 
Depths  of  cell,  2,  5,  9, 18,  27,  and  27  mm.  The  upper  strip  was  exposed 
directly  to  the  ultra-violet  spark  lines. 


DESCRIPTION    OF    PLATES.  105 

PLATE  33.  A.  Samarium  Nitrate  in  Water.  Concentration,  1.06  normal.  Depths  of  cell, 
1, 4, 12,  22,  and  22  mm.  Strips  3  and  5  were  exposed  directly  to  the  ultra- 
violet spark  lines. 

B.  Samarium  Chloride  in  Ethyl  Alcohol  to  which  Water  is  gradually  added. 
The  first  strip  represents  the  absorption  of  a  0.9  normal  aqueous  solution 
of  5.5  mm.  depth.  To  this  solution  were  added  small  amounts  of  water, 
so  that  the  depths  of  cell  were  5.5,  5.6,  5.7,  5.9,  6.0,  6.2,  and  6.4  mm. 
The  change  from  the  first  to  the  second  strip  represents  a  change  from 
the  alcohol  to  the  water  spectra.  After  the  second  strip  there  is  very 
little  change  in  the  spectrum. 

PLATE  34.  A,  Samarium  Chloride  in  Ethyl  Alcohol.  Concentration,  0.9  normal.  Depths 
of  cell,  1,  4,  9,  18,  25,  and  25  mm.  The  upper  strip  was  exposed  directly 
to  the  ultra-violet  spark  lines. 

B.  Samarium  Chloride  in  Ethyl  Alcohol  to  which  Water  is  added.  The  first 
strip  represents  the  absorption  of  a  0.09  normal  solution  in  ethyl  alcohol. 
Succeeding  strips  represent  the  absorption  of  the  same  solution  to  which 
small  quantities  of  water  have  been  added.  Starting  with  the  lowest  strip 
the  depths  of  cell  were:  18,  19,  20,  21.5,  22.5,  25,  and  28  mm. 

PLATE  35.  A.  Cobalt  Bromide  in  Methyl  Alcohol.  Concentration,  0.2  normal.  Depth 
of  cell,  1.0  cm.  Current  in  the  Nernst  glower  0.8  amperes.  Strip  1  was 
exposed  4  minutes  to  the  visible,  and  4  minutes  to  the  violet  and  ultra- 
violet, the  temperature  being  29°  C.  Strip  2  was  exposed  6  minutes  to 
the  whole  spectrum,  at  44°.  Strip  3  was  exposed  6  minutes  at  57°,  and 
strip  4,  15  minutes  at  70°. 

B.  This  spectrogram  shows  the  gradual  oxidization  of  an  aqueous  solution  of 
Uranous  Sulphate  to  which  small  amounts  of  Hydrogen  Peroxide  have 
been  added.  The  plate  shows  the  gradual  decrease  in  intensity  of  the 
uranous  bands,  and  the  corresponding  increase  in  intensity  of  the  uranyl 
bands.  A  spectrogram  of  this  kind  makes  it  very  easy  to  differentiate 
between  the  uranous  and  the  uranyl  bands. 

PLATE  36.  A.  This  plate  represents  the  absorption  of  an  acidified  solution  of  Uranous 
Chloride,  dissolved  in  equal  volumes  of  Water  and  Methyl  Alcohol 
(strip  1)  to  which  was  added  a  concentrated  solution  of  Calcium  Nitrate 
dissolved  in  two  parts  of  Water  and  three  parts  of  Methyl  Alcohol  (suc- 
ceeding strips).  The  original  film  shows  very  clearly  the  selective  action 
of  the  calcium  nitrate  on  the  water  and  alcohol  bands,  the  water  bands 
becoming  much  weaker,  whereas  the  alcohol  bands  remain  of  about  con- 
stant intensity. 

B.  Uranous  Acetate  in  Water  to  which  Nitric  Acid  is  added.  The  first  four 
strips  represent  uranous  acetate  in  water  for  different  depths  of  cell, 
the  depth  of  cell  in  strip  4  being  2.0  cm.  The  succeeding  strips  show  the 
absorption  of  the  same  solution  as  that  used  in  strip  4,  increasing  amounts 
of  nitric  acid  having  been  added.  This  spectrogram  is  then  a  spectro- 
graph  of  the  transformation  of  uranous  acetate  into  uranous  nitrate,  and 
then  the  oxidization  of  uranous  nitrate  to  uranyl  nitrate. 

PLATE  37.  A.  Uranous  Chloride  in  Water  to  which  increasing  amounts  of  Nitric  Acid  are 
added.  The  first  strip  was  accidentally  exposed  a  short  time  directly  to 
the  Nernst  glower.  This  is  a  spectrophotograph  of  the  chemical  reaction 
represented  by  uranous  chloride  being  converted  into  uranous  nitrate. 
B.  Uranous  Chloride  in  equal  parts  of  Water  and  Methyl  Alcohol  (strip  1)  to 
which  Nitric  Acid  is  added  (strips  2,  3,  and  4),  and  to  which  Hydrogen 
Peroxide  is  added  (strip  5).  This  spectrogram  shows  how  the  water 
and  alcohol  bands  of  uranous  chloride  are  changed  to  the  nitrate 
bands,  and  how  these  in  turn  are  replaced  by  the  uranyl  nitrate  bands. 
The  uranous  nitrate  bands  are  seen  to  be  very  different  from  the  chlo- 
ride bands. 


106  DESCRIPTION    OF    PLATES. 

PLATE  38.  A.  Uranous  Chloride  in  equal  parts  by  volume  of  Water  and  Methyl  Alcohol 
(strip  1)  to  which  is  added  increasing  amounts  of  Sodium  Chlorate  dis- 
solved in  equal  volumes  of  Water  and  Methyl  Alcohol  (succeeding  strips). 
This  spectrogram  shows  very  little  of  any  selective  action  on  the  uranous 
chloride  water  and  alcohol  bands. 

B.  Uranous  Chloride  in  equal  volumes  of  Water  and  Methyl  Alcohol  (strip  1) 
to  which  Potassium  Chlorate  in  Water  and  Methyl  Alcohol  is  added 
in  increasing  amounts  (strips  2,  3,  4,  and  5),  and  to  which  Hydrogen 
Peroxide  is  added  (strip  6).  This  spectrogram  shows  the  selective  action 
of  potassium  chlorate  on  the  uranous  chloride  water  and  methyl  alcohol 
bands.  The  water  bands  are  seen  to  decrease  in  intensity,  while  the 
alcohol  bands  increase  in  intensity.  In  this  example  the  addition  of 
hydrogen  peroxide  seems  to  have  oxidized  only  the  alcoholated  uranous 
chloride. 

PLATE  39.  A.  Uranous  Chloride  in  equal  volumes  of  Water  and  Methyl  Alcohol  (strip  1) 
to  which  is  added  Sodium  Chlorate  in  equal  volumes  of  Water  and  Methyl 
Alcohol  (strip  2)  in  one  case,  and  Potassium  Chlorate  in  the  other  (strip 
3).  The  last  strip  represents  the  absorption  of  uranous  chloride  in 
methyl  alcohol  and  ether.  This  plate  shows  the  selective  action  of  the 
above  salts  on  the  water  and  alcohol  bands. 

B.  Uranous  Chloride  in  equal  volumes  of  Water  and  Alcohol  to  which  is  added 
Calcium  Nitrate  in  2  parts  Water  and  3  parts  Methyl  Alcohol  (strip  1); 
in  1  part  Water  and  1  part  Methyl  Alcohol  (strip  2);  and  in  pure  Water 
(strip  3).  A  corresponding  addition  of  potassium  nitrate  was  made, 
the  potassium  nitrate  being  dissolved  in  2  parts  water  and  3  parts 
methyl  alcohol  (strip  4),  1  part  water  and  1  of  alcohol  (strip  5)  and  in 
pure  water  (strip  6) .  The  last  strip  represents  the  absorption  of  uranous 
chloride  itself  in  equal  parts  of  water  and  methyl  alcohol.  This  spec- 
trogram shows  the  selective  action  of  the  salts  on  the  uranous  water  and 
alcohol  bands.  The  selective  action  is  particularly  marked  in  the  case  of 
potassium  nitrate.  The  presence  of  this  salt  seems  to  weaken  the  alcohol 
bands  much  less  than  the  water  bands,  the  proportion  of  water  and  alcohol 
present  being  kept  constant. 

PLATE  40.  A.  Uranous  Bromide  in  Water  to  which  Methyl  Alcohol  is  added.  The  con- 
centration of  the  aqueous  solution  was  0.5  normal,  and  the  percentages 
of  alcohol  in  the  solution,  starting  with  the  first  strip,  were:  0,  24,  39, 
49,  56,  and  62.  This  spectrogram  shows  that  in  the  case  of  uranous 
bromide  at  this  temperature  and  concentration  (the  solution  also  con- 
tains zinc  bromide)  it  is  necessary  that  the  amount  of  alcohol  required 
to  make  the  water  and  alcohol  bands  have  approximately  the  same  inten- 
sity is  about  1  Yi  times  that  of  the  water  present. 

B.  Uranous  Chloride  in  acidified  (Hydrochloric  Acid)  Ethyl  Ester  to  which 
Ethyl  Alcohol  is  added.  The  absorption  of  the  ester  solution  is  very 
similar  to  that  of  an  aqueous  solution.  The  spectrogram  shows  the  much 
greater  absorbing  power  of  the  ethyl  alcohol  solution  compared  with  the 
ester  solution,  the  amount  of  uranous  chloride  being  kept  constant. 

PLATE  41.  A.  Uranous  Chloride  in  Water  and  Methyl  Alcohol  (strip  1)  to  which  are  added 
increasing  amounts  of  Calcium  Nitrate  in  2  parts  Water  and  3  parts 
Methyl  Alcohol  (strips  2,  3,  4),  and  finally  Hydrogen  Peroxide  (strip  5). 
The  spectrogram  shows  that  the  original  solution  was  almost  entirely 
free  from  uranyl  chloride;  that  the  addition  of  calcium  nitrate  had  a 
marked  selective  action  on  the  uranous  bands,  the  water  bands  being 
greatly  decreased  in  intensity  while  the  alcohol  bands  became  more 
intense.  The  addition  of  hydrogen  peroxide  causes  the  complete  disap  - 
pearance  of  the  uranous  bands  and  the  appearance  of  the  uranyl  bands. 
B.  Uranous  Bromide  in  2  parts  Water  and  3  parts  Methyl  Alcohol  (strip  1) 
to  which  Hydrogen  Peroxide  (2  parts  of  a  3  per  cent  Hydrogen  Peroxide 
solution  in  Water  with  3  parts  of  Methyl  Alcohol)  was  added  5  drops  at 
a  time  (strips  2,  3,  4,  5,  6,  and  7).  Strip  1  shows  that  the  oxidization  of 
the  uranous  chloride  by  the  hydrogen  peroxide  is  the  same,  as  indicated 
either  by  the  intensity  of  the  water  bands  or  the  alcohol  bands. 


DESCRIPTION    OF    PLATES.  107 

PLATE  42.  A.  Uranous  Bromide  in  7  parts  Water  and  12  parts  Methyl  Alcohol  (strip  1) 
to  which  are  added  10  (strip  2),  20  (strip  3),  40  (strip  4),  and  80  (strip  5) 
drops  of  a  concentrated  solution  of  Calcium  Nitrate  in  Water.  This 
spectrogram  shows  that  in  this  case  the  water  bands  are  intensified  and 
also  changed  in  character,  the  two  red  water  bands  having  then-  relative 
intensities  greatly  changed.  The  percentages  of  water  present,  start- 
ing with  strip  1,  were:  37,  43,  52,  64,  and  75. 

B.  Uranous  Chloride  in  Ether  and  Methyl  Alcohol  to  which  increasing  amounts 
of  Hydrogen  Peroxide  were  added. 

PLATE  43.  A.  Uranous  Chloride  in  Water  and  Methyl  Alcohol  to  which  Hydrogen  Per- 
oxide is  gradually  added.     This  spectrogram  shows  the  simultaneous 
oxidization  of  the  hydrate  and  alcoholate  of  uranous  chloride. 
B.  Uranous  Bromide  in  Water  and  Methyl  Alcohol  to  which  Potassium  Chlo- 
rate in  Water  and  Methyl  Alcohol  was  gradually  added. 

PLATE  44.  A.  Uranous  Chloride  in  Water  and  Acetone  to  which  Hydrogen  Peroxide  is 

gradually  added. 

B.  Uranous  Bromide  in  Glycerol  to  which  Hydrogen  Peroxide  is  gradually 
added. 

PLATE  45.  A.  Uranous  Bromide  in  Water  and  Methyl  Alcohol  to  which  Nitric  Acid  is 

added. 

B.  Uranous  Chloride  in  Acetone  and  Methyl  Alcohol  to  which  Nitric  Acid  is 
added. 

PLATE  46.  A.  Uranous  Bromide  in  7  parts  Water  and  12  parts  Methyl  Alcohol  (strip  1) 
to  which  is  added  Potassium  Nitrate  in  2  parts  Water  and  3  parts  Methyl 
Alcohol  (strips  2  and  3),  and  corresponding  strips  (4,  5,  and  6)  where 
Calcium  Nitrate  is  added  instead  of  Potassium  Nitrate.  This  spectro- 
gram shows  the  selective  action  of  these  salts  on  the  water  and  alcohol 
bands,  the  water  bands  having  practically  disappeared  in  strips  3  and  6. 
B.  Uranous  Sulphate  in  Water  to  which  Nitric  Acid  is  added  in  increasing 
amounts. 

PLATE  47.  A.  Uranous  Bromide  in  7  parts  Water  and  12  parts  Methyl  Alcohol  to  which 

increasing  amounts  of  Calcium  Nitrate  in  Methyl  Alcohol  are  added. 
B.  Uranous  Bromide  in  2  parts  Water  and  3  parts  Methyl  Alcohol  to  which 
increasing  amounts  of  Sodium  Perchlorate  in  Methyl  Alcohol  are  added. 
These  strips  of  A  and  B  show  the  selective  action  of  the  calcium  nitrate 
and  sodium  perchlorate  on  the  water  and  alcohol  bands,  the  water  bands 
practically  disappearing.  In  this  case  part  of  the  effect  may  be  due  to 
the  increased  percentage  of  alcohol  present. 

PLATE  48.  A.  Uranous  Sulphate  in  Sulphuric  Acid  to  which  Nitric  Acid  is  added.     No 

oxidization  takes  place. 

B.  Uranyl  Bromide  in  Water  to  which  Nitric  Acid  is  added.  The  two  upper 
strips  represent  the  absorption  of  a  solution  of  uranyl  chloride  to  which 
were  added  acetic  acid  and  zinc,  to  find  whether  uranous  acetate  or 
uranous  chloride  would  be  formed,  and  in  what  amounts. 

PLATE  49.  A .  Uranous  Bromide  in  Water  and  Methyl  Alcohol. 

B.  The  first  three  strips  represent  the  oxidization  of  an  aqueous  solution  of 
Uranous  Sulphate  by  Hydrogen  Peroxide.  The  other  four  strips  rep- 
resent the  oxidization  of  a  Sulphuric  Acid  solution  of  Uranous  Sulphate 
by  Hydrogen  Peroxide. 

PLATE  50.  A,  Cobalt  Chloride  in  Methyl  Alcohol.  Concentration,  0.01  normal.  Depth 
of  cell,  10  cm.  Starting  with  the  lowest  strip  the  temperatures  are:  30°, 
45°,  55°,  70°,  and  80°. 

B.  Cobalt  Bromide  in  Methyl  Alcohol.  Concentration,  0.01  normal.  Depth 
of  cell,  10  cm.  Starting  with  the  lowest  strip  the  temperatures  are:  34°, 
44°,  55°,  66°,  81°,  and  100°. 

PLATE  51.  A.  Cobalt  Bromide  in  Methyl  Alcohol.  Concentration,  0.1  normal.  Depth 
of  cell,  1.0  cm.  Starting  with  the  lowest  strip  the  temperatures  are:  31°, 
46°,  58°,  64°,  68°,  and  72°. 

B.  Cobalt  Chloride  in  Methyl  Alcohol.  Concentration,  0.1  normal.  Depth 
of  cell,  1.0  cm.  Starting  with  the  lowest  strip  the  temperatures  are:  23°, 
37°,  47°,  55°,  62°,  73°,  and  93°. 


108 


DESCRIPTION    OF    PLATES. 


PLATE  52.  A.  Neodymium  Chloride  in  Water  (8  per  cent)  and  Ethyl  Alcohol.  Concentra- 
tion, 0.3.  Depth  of  cell,  1.0  cm.  The  exposures  were  started  at  40°  and 
ended  at  80°  C.,  the  temperature  being  gradually  increased  in  the  interim. 
B.  Neodymium  Chloride  in  Water  and  Alcohol.  Concentration,  0.1  normal. 
Depth  of  cell,  1.0  cm.  Range  of  temperature,  starting  from  lowest 
strip,  20°  to  85°  C. 

PLATE  53.  A.  Neodymium  Chloride  in  Methyl  Alcohol.  Concentration,  0.2  normal. 
Depth  of  cell,  1.0  cm.  Temperatures,  25°,  40°,  55°,  and  70°  C. 

B.  Uranous  Chloride  in  Water.  Range  of  temperature  from  30°  to  about  80°  C. 

C.  Neodymium  Bromide  in  Water  (8  per  cent)  and  Methyl  Alcohol.   Concentra- 

tion, 0.2  normal.    Range  of  temperature,  30°  to  80°  C. 
PLATE  54.  A.  Neodymium   Chloride   in   Methyl  Alcohol.     Concentration,   0.1   normal. 

Depth  of  cell,  10  cm.    Temperatures,  26°,  40°,  55°,  78°,  and  85°  C. 
B.  Neodymium   Bromide  in   Methyl   Alcohol.     Concentration,   0.1   normal. 
Depth  of  cell,  10  cm.    Temperatures,  25°,  35°,  44°,  60°,  82°,  100°,  and 
120°  C.    At  the  highest  temperature  a  precipitate  was  formed. 
PLATE  55.  A.  Neodymium  Bromide  in  Water.     Concentration,  1.66  normal.     Depth  of 

cell,  1.0  cm.    Temperatures,  20°,  40°,  60°,  80°,  and  93°  C.  . 
B.  Neodymium  Chloride  in  Water.     Concentration,  2.05  normal.     Depth  of 

cell,  1.0  cm.    Temperatures,  20°,  50°,  and  75°  C. 
Neodymium  Nitrate  in  Water.     Concentration,  2.15  normal.     Depth  of 

cell,  1.0  cm.    Temperatures,  20°,  75°,  and  95°  C. 
PLATE  56.  A.  Neodymium  Chloride  in  Acetone,  10°  and  70°  C. 
Neodymium  Chloride  in  Ether,  10°  C. 
Neodymium  Chloride  in  Ethyl  Alcohol,  10°  and  70°  C. 
Neodymium  Chloride  in  Ethyl  Alcohol  and  Hydrochloric  Acid  at  10°  and 

70°  C. 
B.  Neodymium  Nitrate  in  Nitric  Acid,  10°  and  50°  C. 

Neodymium  Chloride  in  Water  (8  per  cent)  and  Methyl  Alcohol  at  10° 

and  70°  C. 

Neodymium  Nitrate  in  Water  (8  per  cent)  and  Acetone  at  10°  and  60°  C. 
Neodymium  Chloride  in  Water  (40  per  cent)  and  Ethyl  Alcohol  at  10°  C. 
Neodymium  Chloride  in  Water  (40  per  cent)  and  Glycerol  at  10°  C. 
PLATE  57.  A.  Neodymium  Nitrate  in  Water  and  Methyl  Alcohol.    Concentration,  0.25 

normal.     The  variable  here  is  the  percentage  of  water. 

B.  Neodymium  Bromide  in  Water  (8  per  cent)  and  Methyl  Alcohol.  Concen- 
tration, 0.2  normal.  Depth  of  cell,  1.0  cm.  Temperature  range,  25°  to 
115°  C. 

PLATE  58.  A.  Neodymium  Nitrate  in  Water  (14  per  cent)  and  Methyl  Alcohol.  Concen- 
tration, 0.3  normal.  Depth  of  cell,  1.0  cm.  Temperature  range,  25° 
to  115°  C. 

B.  Neodymium  Bromide  in  Water  (8  per  cent)  and  Ethyl  Alcohol.    Concentra- 
tion, 0.2  normal.     Depth  of  cell,  1.0  cm.     Temperature  range,  25°  to 
87°  C. 
PLATE  59.  A.  Neodymium  Chloride  in  Water  at  10°  and  90°  C. 

Neodymium  Chloride  in  Hydrochloric  Acid  at  10°  and  90°  C. 
Neodymium  Chloride  in  Methyl  Alcohol. 

Neodymium  Chloride  and  Sodium  Chlorate  in  Methyl  Alcohol. 
B.  Neodymium  Acetate  in  Water  at  10°  and  90°  C. 

Neodymium  Chloride  in  Acetic  Acid  at  10°  and  90°  C. 
Neodymium  Acetate  in  Acetic  Acid  at  10°  and  90°  C. 
Neodymium  Acetate  in  Methyl  Ester  and  Acetic  Acid  at  10°  and  90°  C. 
PLATE  60.  A.  Erbium  Chloride  in  Water  at  20°,  30°,  85°,  and  115°  C. 

B.  Neodymium  Chloride  in  Water.     Concentration,  0.2  normal.     Depth  of 

cell,  10  cm.    Temperatures,  20°,  50°,  85°,  and  115°  C. 

C.  Neodymium  Nitrate  in  Tertiary  Butyl  Alcohol.    Concentration,  0.2  normal. 

Depth  of  cell,  1.0  cm.    Temperatures,  25°,  50°,  and  65°  C. 
Neodymium  Nitrate  in  Isobutyl  Alcohol  at  20°,  75°,  and  100°  C. 


DESCRIPTION    OF    PLATES.  109 

PLATE  61.  A.  Uranyl  Chloride  in  Isobutyl  Alcohol.    Concentration,  0.005  normal.    Depth 

of  cell,  10  cm.    Temperatures,  18°,  40°,  60°,  80°,  100°,  and  90°  C. 
B.  Erbium  Chloride  in  Methyl  Alcohol.    Depth  of  cell,  10  cm.    Temperatures, 
20°,  45°,  75°,  110°,  125°,  and  165°  (after  a  precipitate  had  been  formed). 
PLATE  62.  A.  Uranyl  Chloride  in  Isobutyl  Alcohol.    Concentration,  0.076  normal.    Depth 

of  cell,  10  cm.    Temperatures,  20°,  60°,  85°,  and  115°  C. 
B.  Uranyl  Nitrate  in  Isobutyl  Alcohol.    Concentration,  0.033  normal.    Depth 

of  cell,  10  cm.    Temperatures,  20°,  50°,  80°,  100°,  and  115°  C. 

PLATE  63.  A.  Uranyl  Nitrate  in  Methyl  Alcohol.     Concentration,  0.2  normal.     Depth 
of  cell,  1.0  cm.     Temperatures,  20°,  100°,  135°,  145°  (precipitate),  and 
160°  C. 
B.  Uranyl  and  Calcium  Chlorides  in  Methyl  Ester  at  20°,  45°,  and  85°  C. 

Uranyl  and  Calcium  Chlorides  in  Methyl  Alcohol  at  20°,  50°,  and  95°  C. 
PLATE  64.  A.  Uranyl  Chloride  in  Methyl  Ester.    Concentration,  0.005  normal.    Depth 
of  cell,  10  cm.    Temperatures,  20°,  45°,  70°,  90°,  110°,  135°,  and  140°  C. 
B.  Uranvl  Nitrate  in  Propyl  Alcohol.    Concentration,  0.005  normal.     Depth 
of  cell,  10  cm.     Temperatures,  20°,  40°,  65°,  85°,  105°,  115°,  130°,  and 
145°  C. 
PLATE  65.  A.  Uranyl  Chloride  in  Propyl  Alcohol.     Concentration,  0.01  normal.     Depth 

of  cell,  10  cm.    Temperatures,  22°,  45°,  70°,  90°,  and  100°  C. 
B.  Uranyl  Chloride  in  Methyl  Alcohol.    Concentration,  0.005  normal.    Depth 

of  cell,  10  cm.    Temperatures,  20°,  45°,  65°,  85°,  110°,  120°,  and  145°  C. 
PLATE  66.  A.  Uranyl  Chloride  in  Methyl  Ester.    Concentration,  0.034  normal.    Uranoua 
Chloride  in  Methyl  Ester  (strips  2  and  3);  Uranyl  Nitrate  in  Methyl 
Ester;  Uranyl  Chloride  in  Methyl  Alcohol;  and  Uranyl  Nitrate  in  Methyl 
Alcohol. 
B.  Uranyl  Nitrate  in  Methyl  Ester.     Concentration,  0.005  normal.     Depth 

of  cell,  10  cm.    Temperatures,  20°,  50°,  75°,  100°,  125°,  and  145°  C. 
PLATE  67.  A.  Uranous  Sulphate  in  Sulphuric  Acid  at  10°  and  90°  C. 
Uranous  Sulphate  in  Water  at  10°  and  90°  C. 
Uranous  Chloride  in  Water  and  Methyl  Alcohol  at  10°  and  70°  C. 
B.  Uranyl  Nitrate  in  Nitric  Acid  at  10°  and  70°  C. 

Uranyl  Chloride  in  Hydrochloric  Acid  at  10°  and  80°  C. 
Uranyl  Sulphate  in  Water  at  10°  and  80°  C. 
Uranyl  Sulphate  in  Sulphuric  Acid  at  10°  and  70°  C. 


INDEX. 


Absorption  and  emission  centers — 

And  the  ionization  theory 2 

Of  light  and  heat 1 

Absorption  spectra — 

Of  benzene  and  its  derivatives 16 

Of  organic  compounds 8 

Of  various  salts  in  solution,  map- 
ping the 31 

Acetone — 

Neodymium  acetate  in 40 

Neodymium  nitrate  in 39 

Solution  of  neodymium  nitrate 80 

Solution  of  uranous  chloride 82 

Solution  of  uranyl  chloride 81 

Uranyl  nitrate  in 44 

Acid  solutions  of  neodymium  salts 84 

Acids,  strengths  of,  possible  method  of 

measuring 62 

Aggregates  and  their  properties 95 

Effect  of  temperature  on 83 

Alcohols,  samarium  chloride  in 49 

Aluminium  and  calcium  chromates 33 

Anthracene,     neodymium     chloride     in 

ethyl  acetate  and 56 

Apparatus  and  methods,  experimental .  .  27 

Arcs  and  flames,  emission  centers  of. ...  6 

Bands,  uranous  and  uranyl 94 

Benzene — 

And     its     derivatives,    absorption 

spectra  of 16 

Theories 25 

Bichromate — 

And  chromat  e  of  lithium 33 

Of  copper 33 

Butyl  alcohol — 

Neodymium  chloride  in 36 

Neodymium  nitrate  in 38 

Uranyl  chloride  in 43 

Calcium — 

And  aluminium  chromates 33 

Ferricyanide    and    calcium    ferro- 

cyanide 32 

Ferrocyanide    and    calcium    ferri- 

cyanide 32 

Canal-ray  spectra,  carriers  of 4 

Carriers — 

Of  canal-ray  spectra 4 

Of  spark  spectra 5 

Catalytic  action  of  light 6 

Centers — 

Absorption   and   emission   of  light 

and  heat 1 

Absorption,  of  uranium  spectra. ...  45 
Emission  and  absorption,  and  the 

ionization  theory 2 

Emission,  of  flames  and  arcs 6 

110 


Chromate — 

And  bichromate  of  lithium 33 

Potassium  nickel 33 

Chromates — 

And  cyanides,  absorption  of  certain  31 

Of  calcium  and  aluminium 33 

Chromophores,  theory  of 10 

Copper  bichromate 33 

Cyanides  and  chromates,  absorption  of 

certain 31 

Description  of  plates 101 

Discussion  of  results 87 

Dynamic  isomerism,  theory  of 18 

j   Dysprosium — 

Absorption  spectrum  of 46 

Acetate  in  water 48 

Chloride  in  ethyl  alcohol 47 

Chloride  in  methyl  alcohol 47 

Chloride  in  water 47 

Ether— 

Neodymium  chloride  in 37 

Uranyl  chloride  in 43 

Ethyl  alcohol — 

Dysprosium  chloride  in 47 

Solution  of  neodymium  chloride 77 

Ethyl  ester,  neodymium  nitrate  in ....  39 

Emission  and  absorption  centers — 

And  the  ionization  theory 2 

Of  light  and  heat 1 

Emission — 

Centers  of  flames  and  arcs 6 

Spectra  of  organic  compounds 7 

Erbium — 

Chloride  in  water 80 

Salts,  absorption  of  solutions  of ....  33 

Experimental  methods  and  apparatus . .  27 

Flames  and  arcs,  emission  centers  of .  . .  6 

Ferrocyanide  and  ferricyanide  of  calcium  32 
Formamide — 

Neodymium  acetate  in 40 

Uranyl  chloride  in 44 

Gadolinium — 

Absorption  spectrum  of 46 

Chloride  in  ethyl  alcohol 46 

Chloride  in  water 46 

Heat,  absorption  and  emission  centers  of  1 
Hydrochloric    acid    solution    of   uranyl 

chloride 86 

Ionization  theory  and  absorption  and 

emission  centers 2 

Ions,  are  they  factors  in  the  absorption 

of  light 62 


INDEX. 


Ill 


Isobutyl  alcohol — 

Neodymium  chloride  in 37 

Neodymium  nitrate  in 39 

Solution  of  neodymium  nitrate...  .  79 
Solution  of  uranyl  chloride  and 

nitrate .". 81 

Uranous  chloride  in 45 

Uranyl  chloride  in 43 

Isomerism,  dynamic,  theory  of 18 

Isoprophyl  alcohol — 

Xeodymium  chloride  in 36 

Xeodymium  nitrate  in 38 

Uranyl  chloride  in 43 

Isorropesis 22 

Light- 
Absorption  and  emission  centers  of, 

and  heat 1 

Catalytic  action  of 6 

Lithium  chromate  and  bichromate 33 

Mapping — 

Of    absorption   spectra   of    various 

salts  in  solution 31 

Of  spectra 87 

Mass,  spectroscopic    evidence    for    the 

effect  of 71 

Methods  and  apparatus,  experimental. .  27 

Methyl  alcohol — 

Dysprosium  chloride  in 47 

Solution  of  neodymium  bromide . .  77 

Solution  of  neodymium  chloride . .  78 

Solution  of  uranous  chloride 82 

Uranous  chloride  in 45 

Uranyl  chloride  in 44 

Uranyl  nitrate  in 44 

Naphthalene,  spectrum  of 7 

Neodymium — 

Acetate  in  acetone 40 

Acetate  in  formamide 40 

Bromide  in  methyl  alcohol 79 

Bromide  in  water  and  methyl  alcohol  77 
Chloride  as  a  methyl  alcoholate ....  35 
Chloride,  bromide  and  nitrate  in 

water 77 

Chloride  in  butyl  alcohol 36 

Chloride     in     ethyl     acetate     and 

anthracene 56 

Chloride  in  isobutyl  alcohol 37 

Chloride  in  isoprophyl  alcohol 36 

Chloride  in  methyl  alcohol 78 

Chloride  in  propyl  alcohol 36 

Chloride  in  water 35.  37 

Chloride  in  water  and  ethyl  alcohol  77 

Xltrate  in  acetone -. .  39 

Nitrate  in  butyl  alcohol 38 

Nitrate  in  ethyl  ester 39 

Nitrate  in  isobutyl  alcohol 39 

Nitrate  in  isopropyl  alcohol 38 

Nitrate  in  propyl  alcohol 38 

Salts,    absorption    of    solutions    of 

certain 34 

Salts  in  acid  solutions 84 

Spectra,  summary  of 40 


PAOK 

Xitnc  acid — 

Action  on  uranous  acetate 65 

Oxidation  of  uranous  salts  by 64 

Nitric  acid  solution  of  uranyl  nitrate. . .  86 

Organic  compound — 

Absorption  spectra 8 

Emission  spectra  of 7 

Oxidation — 

Of  uranous  bromide  by  hydrogen 

peroxide ." 61 

Of  uranous  chloride  by  hydrogen 

peroxide 58 

Of  uranous  chloride  in  hydrochloric 

acid  by  hydrogen  peroxide 60 

Of  uranous  salts  by  nitric  acid ....  64 

Of  uranous  sulphate 61 

Of  uranous  to  uranyl  salts  in  solution  58 

Phosphorescence  of  salts 54 

Plates,  description  of 101 

Potassium  nickel  chromate 33 

Properties  of  aggregates 95 

Propyl  alcohol — 

Neodymium  chloride  in 36 

Neodymium  nitrate  in 38 

Solution  of  uranyl  nitrate 81 

Uranous  chloride  in 44 

Uranyl  chloride  in 43 

Uranyl  nitrate  in 44 

Reactions,    chemical,    spectrophotogra- 

phy  of 52 

Reduction — 

Of  uranyl  chloride  in  methyl  ester  69 

Of  uranyl  salts  in  solution 69 

Selective,  of  uranyl  aggregates 70 

Results,  summary  and  general  discus- 
sion of 87 

Samarium — 

Absorption  spectrum  of 48 

Chloride  in  methyl  and  ethyl  alcohols  49 

Chloride  in  water 48 

Chloride  in  water  and  ethyl  alcohol  50 

Nitrate  in  water 49 

|   Schumann  waves 6 

Selective  reduction  of  uranyl  aggregates  70 

Solvates— 

Effect  of  temperature  on  the  rela- 
tive intensity  of  solvate  bands . .   74 
Selective  action  of  chemical  reagents 
on 66 

Solvation 92 

Solvent,  influence  of 15 

Spark  spectra,  carriers  of 5 

Spectra- 
Carriers  of  canal-ray 4 

Carriers  of  spark 5 

Emission,  of  organic  compounds. ..     7 
Mapping  of 87 

Spectrophotography   of  chemical   reac- 
tions    51 

Spectroscopic  evidence  for  the  effect  of 

mass 71 

Stark's  theory 23 


112 


INDEX. 


Strengths  of  acids,  possible  method  of 

measuring 62 

Summary — 

And  general  discussion  of  results . .  87 
Of  neodymium  spectra 40 

Sulphuric  acid  solution — 

Of  uranous  sulphate 85 

Of  uranyl  sulphate 86 

Temperature,  effect  of — 

On  absorption  spectra 73,  98 

On  aggregates 83 

On    relative    intensity    of    solvate 
bands 74 

Theory — 

Of  absorption  spectra 89 

Of  dynamic  isomerism 18 

Unit  of  absorption 8 

Uranium — 

Absorption  spectrum  of  solutions  of 

certain  salts  of 43 

Spectra,  absorption  centers  of 45 

Uranous — 

Acetate,  effect  of  the  addition  of 

nitric  acid 65 

And  uranyl  bands 57,  94 

Bromide,    oxidation    by    hydrogen 

peroxide 61 

Chloride  in  acetone 82 

Chloride  in  isobutyl  alcohol 45 

Chloride  in  methyl  ester 45 

Chloride  in  propyl  alcohol 44 


Uranous  chloride  in  water  and  methyl 

alcohol 82 

Chloride    oxidation    by    hydrogen 

peroxide 58 

Chloride     oxidized     by     hydrogen 

peroxide 60 

Oxidized  to  uranyl  salts  in  solution  58 
Salts,  oxidation  by  nitric  acid ....   64 

Sulphate  in  sulphuric  acid 85 

Sulphate,  oxidation  of 61 

Uranyl — 

Aggregates,  selective  reduction  of.  .   70 

And  uranous  bands 57,  94 

Chloride  and  nitrate  in  methyl  ester  81 

Chloride  in  acetone 81 

Chloride  in  butyl  alcohol 43 

Chloride  in  ether 43 

Chloride  in  ethyl  ester 44 

Chloride  in  formamide 44 

Chloride  in  hydrochloric  acid 86 

Chloride  in  isobutyl  alcohol 43,  81 

Chloride  in  isopropyl  alcohol 43 

Chloride  in  methyl  ester 44 

Chloride  in  methyl  ester,  reduction  of  69 

Chloride  in  propyl  alcohol 43 

Nitrate  in  acetone 44 

Nitrate  in  isobutyl  alcohol 81 

Nitrate  in  methyl  ester 44,  81 

Nitrate  in  nitric  acid 86 

Nitrate  in  propyl  alcohol 44,  81 

Salts  in  solution,  reduction  of 69 

Salts,  reduction  in  solution 69 

Sulphate  in  sulphuric  acid 86 


PLATE     1 


PLATE  2 


PLATE  5 


PLATE  6 


m 


c 


' 


- 


m-m 


- 


QQ 


Ill 


PLATE  25 


OQ 


•Hi 


PLATE  29 


DQ 


PLATE  30 


PLATE  31 


PLATE  37 


PLATE  38 


= 


- 


QQ 


PLATE  52 


PLATE  53 


* 


? 


pq 


PLATE 


;; 


PLATE  65 


PLATE  66 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 

Los  Angeles 
This  book  is  DUE  on  the  last  date  stamped  below. 


CHEMISTRY  LIBRARY 
825-3342 

MAY  i  6    1991 


HEMISTRY  LIBRARY 
825-3342 


315 


UCLA-Chemistry  Library 

QC437J71abs 


L  006  548  282  0 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


AA    001042855    5 


UNIVERSITY  nf  CALIFORNIA 


LIBRARY 


